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Storage Administration Guide
Deploying and configuring single-node storage in RHEL 7
Abstract
Chapter 1. Overview
1.1. New Features and Enhancements in Red Hat Enterprise Linux 7
eCryptfs not included
System Storage Manager
XFS Is the Default File System
File System Restructure
/bin
, /sbin
, /lib
, and /lib64
are now nested under /usr
.
Snapper
Btrfs (Technology Preview)
Note
NFSv2 No Longer Supported
Part I. File Systems
Note
Chapter 2. File System Structure and Maintenance
- Shareable and unsharable files
- Shareable files can be accessed locally and by remote hosts. Unsharable files are only available locally.
- Variable and static files
- Variable files, such as documents, can be changed at any time. Static files, such as binaries, do not change without an action from the system administrator.
2.1. Overview of Filesystem Hierarchy Standard (FHS)
- Compatibility with other FHS-compliant systems
- The ability to mount a
/usr/
partition as read-only. This is crucial, since/usr/
contains common executables and should not be changed by users. In addition, since/usr/
is mounted as read-only, it should be mountable from the CD-ROM drive or from another machine via a read-only NFS mount.
2.1.1. FHS Organization
Note
2.1.1.1. Gathering File System Information
df
Command
df
command reports the system's disk space usage. Its output looks similar to the following:
Example 2.1. df
Command Output
Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/VolGroup00-LogVol00 11675568 6272120 4810348 57% / /dev/sda1 100691 9281 86211 10% /boot none 322856 0 322856 0% /dev/shm
df
shows the partition size in 1 kilobyte blocks and the amount of used and available disk space in kilobytes. To view the information in megabytes and gigabytes, use the command df -h
. The -h
argument stands for "human-readable" format. The output for df -h
looks similar to the following:
Example 2.2. df -h
Command Output
Filesystem Size Used Avail Use% Mounted on /dev/mapper/VolGroup00-LogVol00 12G 6.0G 4.6G 57% / /dev/sda1 99M 9.1M 85M 10% /boot none 316M 0 316M 0% /dev/shm
Note
/dev/shm
represents the system's virtual memory file system.
du
Command
du
command displays the estimated amount of space being used by files in a directory, displaying the disk usage of each subdirectory. The last line in the output of du
shows the total disk usage of the directory. To see only the total disk usage of a directory in human-readable format, use du -hs
. For more options, see man du
.
Gnome System Monitor
gnome-system-monitor
. Select the File Systems tab to view the system's partitions. The following figure illustrates the File Systems tab.
Figure 2.1. File Systems Tab in GNOME System Monitor
2.1.1.2. The /boot/
Directory
/boot/
directory contains static files required to boot the system, for example, the Linux kernel. These files are essential for the system to boot properly.
Warning
/boot/
directory. Doing so renders the system unbootable.
2.1.1.3. The /dev/
Directory
/dev/
directory contains device nodes that represent the following device types:
- devices attached to the system;
- virtual devices provided by the kernel.
udevd
daemon creates and removes device nodes in /dev/
as needed.
/dev/
directory and subdirectories are defined as either character (providing only a serial stream of input and output, for example, mouse or keyboard) or block (accessible randomly, such as a hard drive or a floppy drive). If GNOME or KDE is installed, some storage devices are automatically detected when connected (such as with USB) or inserted (such as a CD or DVD drive), and a pop-up window displaying the contents appears.
File | Description |
---|---|
/dev/hda | The master device on the primary IDE channel. |
/dev/hdb | The slave device on the primary IDE channel. |
/dev/tty0 | The first virtual console. |
/dev/tty1 | The second virtual console. |
/dev/sda | The first device on the primary SCSI or SATA channel. |
/dev/lp0 | The first parallel port. |
- Mapped device
- A logical volume in a volume group, for example,
/dev/mapper/VolGroup00-LogVol02
. - Static device
- A traditional storage volume, for example,
/dev/sdbX
, where sdb is a storage device name and X is the partition number./dev/sdbX
can also be/dev/disk/by-id/WWID
, or/dev/disk/by-uuid/UUID
. For more information, see Section 25.8, “Persistent Naming”.
2.1.1.4. The /etc/
Directory
/etc/
directory is reserved for configuration files that are local to the machine. It should not contain any binaries; if there are any binaries, move them to /usr/bin/
or /usr/sbin/
.
/etc/skel/
directory stores "skeleton" user files, which are used to populate a home directory when a user is first created. Applications also store their configuration files in this directory and may reference them when executed. The /etc/exports
file controls which file systems export to remote hosts.
2.1.1.5. The /mnt/
Directory
/mnt/
directory is reserved for temporarily mounted file systems, such as NFS file system mounts. For all removable storage media, use the /media/
directory. Automatically detected removable media is mounted in the /media
directory.
Important
/mnt
directory must not be used by installation programs.
2.1.1.6. The /opt/
Directory
/opt/
directory is normally reserved for software and add-on packages that are not part of the default installation. A package that installs to /opt/
creates a directory bearing its name, for example, /opt/packagename/
. In most cases, such packages follow a predictable subdirectory structure; most store their binaries in /opt/packagename/bin/
and their man
pages in /opt/packagename/man/
.
2.1.1.7. The /proc/
Directory
/proc/
directory contains special files that either extract information from the kernel or send information to it. Examples of such information include system memory, CPU information, and hardware configuration. For more information about /proc/
, see Section 2.3, “The /proc Virtual File System”.
2.1.1.8. The /srv/
Directory
/srv/
directory contains site-specific data served by a Red Hat Enterprise Linux system. This directory gives users the location of data files for a particular service, such as FTP, WWW, or CVS. Data that only pertains to a specific user should go in the /home/
directory.
2.1.1.9. The /sys/
Directory
/sys/
directory utilizes the new sysfs
virtual file system specific to the kernel. With the increased support for hot plug hardware devices in the kernel, the /sys/
directory contains information similar to that held by /proc/
, but displays a hierarchical view of device information specific to hot plug devices.
2.1.1.10. The /usr/
Directory
/usr/
directory is for files that can be shared across multiple machines. The /usr/
directory is often on its own partition and is mounted read-only. At a minimum, /usr/
should contain the following subdirectories:
/usr/bin
- This directory is used for binaries.
/usr/etc
- This directory is used for system-wide configuration files.
/usr/games
- This directory stores games.
/usr/include
- This directory is used for C header files.
/usr/kerberos
- This directory is used for Kerberos-related binaries and files.
/usr/lib
- This directory is used for object files and libraries that are not designed to be directly utilized by shell scripts or users.As of Red Hat Enterprise Linux 7.0, the
/lib/
directory has been merged with/usr/lib
. Now it also contains libraries needed to execute the binaries in/usr/bin/
and/usr/sbin/
. These shared library images are used to boot the system or execute commands within the root file system. /usr/libexec
- This directory contains small helper programs called by other programs.
/usr/sbin
- As of Red Hat Enterprise Linux 7.0,
/sbin
has been moved to/usr/sbin
. This means that it contains all system administration binaries, including those essential for booting, restoring, recovering, or repairing the system. The binaries in/usr/sbin/
require root privileges to use. /usr/share
- This directory stores files that are not architecture-specific.
/usr/src
- This directory stores source code.
/usr/tmp
linked to/var/tmp
- This directory stores temporary files.
/usr/
directory should also contain a /local/
subdirectory. As per the FHS, this subdirectory is used by the system administrator when installing software locally, and should be safe from being overwritten during system updates. The /usr/local
directory has a structure similar to /usr/
, and contains the following subdirectories:
/usr/local/bin
/usr/local/etc
/usr/local/games
/usr/local/include
/usr/local/lib
/usr/local/libexec
/usr/local/sbin
/usr/local/share
/usr/local/src
/usr/local/
differs slightly from the FHS. The FHS states that /usr/local/
should be used to store software that should remain safe from system software upgrades. Since the RPM Package Manager can perform software upgrades safely, it is not necessary to protect files by storing them in /usr/local/
.
/usr/local/
for software local to the machine. For instance, if the /usr/
directory is mounted as a read-only NFS share from a remote host, it is still possible to install a package or program under the /usr/local/
directory.
2.1.1.11. The /var/
Directory
/usr/
as read-only, any programs that write log files or need spool/
or lock/
directories should write them to the /var/
directory. The FHS states /var/
is for variable data, which includes spool directories and files, logging data, transient and temporary files.
/var/
directory:
/var/account/
/var/arpwatch/
/var/cache/
/var/crash/
/var/db/
/var/empty/
/var/ftp/
/var/gdm/
/var/kerberos/
/var/lib/
/var/local/
/var/lock/
/var/log/
/var/mail
linked to/var/spool/mail/
/var/mailman/
/var/named/
/var/nis/
/var/opt/
/var/preserve/
/var/run/
/var/spool/
/var/tmp/
/var/tux/
/var/www/
/var/yp/
Important
/var/run/media/user
directory contains subdirectories used as mount points for removable media such as USB storage media, DVDs, CD-ROMs, and Zip disks. Note that previously, the /media/
directory was used for this purpose.
messages
and lastlog
, go in the /var/log/
directory. The /var/lib/rpm/
directory contains RPM system databases. Lock files go in the /var/lock/
directory, usually in directories for the program using the file. The /var/spool/
directory has subdirectories that store data files for some programs. These subdirectories include:
/var/spool/at/
/var/spool/clientmqueue/
/var/spool/cron/
/var/spool/cups/
/var/spool/exim/
/var/spool/lpd/
/var/spool/mail/
/var/spool/mailman/
/var/spool/mqueue/
/var/spool/news/
/var/spool/postfix/
/var/spool/repackage/
/var/spool/rwho/
/var/spool/samba/
/var/spool/squid/
/var/spool/squirrelmail/
/var/spool/up2date/
/var/spool/uucp/
/var/spool/uucppublic/
/var/spool/vbox/
2.2. Special Red Hat Enterprise Linux File Locations
/var/lib/rpm/
directory. For more information on RPM, see man rpm
.
/var/cache/yum/
directory contains files used by the Package Updater, including RPM header information for the system. This location may also be used to temporarily store RPMs downloaded while updating the system. For more information about the Red Hat Network, see https://rhn.redhat.com/.
/etc/sysconfig/
directory. This directory stores a variety of configuration information. Many scripts that run at boot time use the files in this directory.
2.3. The /proc Virtual File System
/proc
contains neither text nor binary files. Because it houses virtual files, the /proc
is referred to as a virtual file system. These virtual files are typically zero bytes in size, even if they contain a large amount of information.
/proc
file system is not used for storage. Its main purpose is to provide a file-based interface to hardware, memory, running processes, and other system components. Real-time information can be retrieved on many system components by viewing the corresponding /proc
file. Some of the files within /proc
can also be manipulated (by both users and applications) to configure the kernel.
/proc
files are relevant in managing and monitoring system storage:
- /proc/devices
- Displays various character and block devices that are currently configured.
- /proc/filesystems
- Lists all file system types currently supported by the kernel.
- /proc/mdstat
- Contains current information on multiple-disk or RAID configurations on the system, if they exist.
- /proc/mounts
- Lists all mounts currently used by the system.
- /proc/partitions
- Contains partition block allocation information.
/proc
file system, see the Red Hat Enterprise Linux 7 Deployment Guide.
2.4. Discard Unused Blocks
- Batch discard operations are run explicitly by the user with the
fstrim
command. This command discards all unused blocks in a file system that match the user's criteria. - Online discard operations are specified at mount time, either with the
-o discard
option as part of amount
command or with thediscard
option in the/etc/fstab
file. They run in real time without user intervention. Online discard operations only discard blocks that are transitioning from used to free.
/sys/block/device/queue/discard_max_bytes
file is not zero.
fstrim
command on:
- a device that does not support discard operations, or
- a logical device (LVM or MD) comprised of multiple devices, where any one of the device does not support discard operations
fstrim -v /mnt/non_discard
fstrim: /mnt/non_discard: the discard operation is not supported
Note
mount
command allows you to mount a device that does not support discard operations with the -o discard
option.
Chapter 3. The XFS File System
- Main Features of XFS
- XFS supports metadata journaling, which facilitates quicker crash recovery.
- The XFS file system can be defragmented and enlarged while mounted and active.
- In addition, Red Hat Enterprise Linux 7 supports backup and restore utilities specific to XFS.
- Allocation Features
- XFS features the following allocation schemes:
- Extent-based allocation
- Stripe-aware allocation policies
- Delayed allocation
- Space pre-allocation
Delayed allocation and other performance optimizations affect XFS the same way that they do ext4. Namely, a program's writes to an XFS file system are not guaranteed to be on-disk unless the program issues anfsync()
call afterwards.For more information on the implications of delayed allocation on a file system (ext4 and XFS), see Allocation Features in Chapter 5, The ext4 File System.Note
Creating or expanding files occasionally fails with an unexpected ENOSPC write failure even though the disk space appears to be sufficient. This is due to XFS's performance-oriented design. In practice, it does not become a problem since it only occurs if remaining space is only a few blocks. - Other XFS Features
- The XFS file system also supports the following:
- Extended attributes (
xattr
) - This allows the system to associate several additional name/value pairs per file. It is enabled by default.
- Quota journaling
- This avoids the need for lengthy quota consistency checks after a crash.
- Project/directory quotas
- This allows quota restrictions over a directory tree.
- Subsecond timestamps
- This allows timestamps to go to the subsecond.
- Extended attributes (
- Default
atime
behavior isrelatime
Relatime
is on by default for XFS. It has almost no overhead compared tonoatime
while still maintaining saneatime
values.
3.1. Creating an XFS File System
- To create an XFS file system, use the following command:
#
mkfs.xfs block_device
- Replace block_device with the path to a block device. For example,
/dev/sdb1
,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a
, or/dev/my-volgroup/my-lv
. - In general, the default options are optimal for common use.
- When using
mkfs.xfs
on a block device containing an existing file system, add the-f
option to overwrite that file system.
Example 3.1. mkfs.xfs
Command Output
mkfs.xfs
command:
meta-data=/dev/device isize=256 agcount=4, agsize=3277258 blks = sectsz=512 attr=2 data = bsize=4096 blocks=13109032, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0 log =internal log bsize=4096 blocks=6400, version=2 = sectsz=512 sunit=0 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0
Note
xfs_growfs
command. For more information, see Section 3.4, “Increasing the Size of an XFS File System”).
Striped Block Devices
mkfs.xfs
chooses an optimal geometry. This may also be true on some hardware RAIDs that export geometry information to the operating system.
mkfs
utility (for ext3, ext4, and xfs) will automatically use this geometry. If stripe geometry is not detected by the mkfs
utility and even though the storage does, in fact, have stripe geometry, it is possible to manually specify it when creating the file system using the following options:
- su=value
- Specifies a stripe unit or RAID chunk size. The
value
must be specified in bytes, with an optionalk
,m
, org
suffix. - sw=value
- Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
#
mkfs.xfs -d su=64k,sw=4 /dev/block_device
Additional Resources
- The mkfs.xfs(8) man page
3.2. Mounting an XFS File System
#
mount /dev/device /mount/point
Note
mke2fs
, mkfs.xfs
does not utilize a configuration file; they are all specified on the command line.
Write Barriers
nobarrier
option:
#
mount -o nobarrier /dev/device /mount/point
Direct Access Technology Preview
Direct Access
(DAX) is available as a Technology Preview on the ext4 and XFS file systems. It is a means for an application to directly map persistent memory into its address space. To use DAX, a system must have some form of persistent memory available, usually in the form of one or more Non-Volatile Dual Inline Memory Modules (NVDIMMs), and a file system that supports DAX must be created on the NVDIMM(s). Also, the file system must be mounted with the dax
mount option. Then, an mmap
of a file on the dax-mounted file system results in a direct mapping of storage into the application's address space.
3.3. XFS Quota Management
noenforce
; this allows usage reporting without enforcing any limits. Valid quota mount options are:
uquota
/uqnoenforce
: User quotasgquota
/gqnoenforce
: Group quotaspquota
/pqnoenforce
: Project quota
xfs_quota
tool can be used to set limits and report on disk usage. By default, xfs_quota
is run interactively, and in basic mode. Basic mode subcommands simply report usage, and are available to all users. Basic xfs_quota
subcommands include:
quota username/userID
- Show usage and limits for the given
username
or numericuserID
df
- Shows free and used counts for blocks and inodes.
xfs_quota
also has an expert mode. The subcommands of this mode allow actual configuration of limits, and are available only to users with elevated privileges. To use expert mode subcommands interactively, use the following command:
#
xfs_quota -x
report /path
- Reports quota information for a specific file system.
limit
- Modify quota limits.
help
.
-c
option, with -x
for expert subcommands.
Example 3.2. Display a Sample Quota Report
/home
(on /dev/blockdevice
), use the command xfs_quota -x -c 'report -h' /home
. This displays output similar to the following:
User quota on /home (/dev/blockdevice) Blocks User ID Used Soft Hard Warn/Grace ---------- --------------------------------- root 0 0 0 00 [------] testuser 103.4G 0 0 00 [------] ...
john
, whose home directory is /home/john
, use the following command:
#
xfs_quota -x -c 'limit isoft=500 ihard=700 john' /home/
limit
subcommand recognizes targets as users. When configuring the limits for a group, use the -g
option (as in the previous example). Similarly, use -p
for projects.
bsoft
or bhard
instead of isoft
or ihard
.
Example 3.3. Set a Soft and Hard Block Limit
accounting
on the /target/path
file system, use the following command:
#
xfs_quota -x -c 'limit -g bsoft=1000m bhard=1200m accounting' /target/path
Note
bsoft
and bhard
count by the byte.
Important
rtbhard
/rtbsoft
) are described in man xfs_quota
as valid units when setting quotas, the real-time sub-volume is not enabled in this release. As such, the rtbhard
and rtbsoft
options are not applicable.
Setting Project Limits
- Add the project-controlled directories to
/etc/projects
. For example, the following adds the/var/log
path with a unique ID of 11 to/etc/projects
. Your project ID can be any numerical value mapped to your project.#
echo 11:/var/log >> /etc/projects
- Add project names to
/etc/projid
to map project IDs to project names. For example, the following associates a project called logfiles with the project ID of 11 as defined in the previous step.#
echo logfiles:11 >> /etc/projid
- Initialize the project directory. For example, the following initializes the project directory
/var
:#
xfs_quota -x -c 'project -s logfiles' /var
- Configure quotas for projects with initialized directories:
#
xfs_quota -x -c 'limit -p bhard=lg logfiles' /var
quota
, repquota
, and edquota
for example) may also be used to manipulate XFS quotas. However, these tools cannot be used with XFS project quotas.
Important
xfs_quota
over all other available tools.
man xfs_quota
, man projid(5)
, and man projects(5)
.
3.4. Increasing the Size of an XFS File System
xfs_growfs
command:
#
xfs_growfs /mount/point -D size
-D size
option grows the file system to the specified size
(expressed in file system blocks). Without the -D size
option, xfs_growfs
will grow the file system to the maximum size supported by the device.
-D size
, ensure that the underlying block device is of an appropriate size to hold the file system later. Use the appropriate resizing methods for the affected block device.
Note
man xfs_growfs
.
3.5. Repairing an XFS File System
xfs_repair
:
#
xfs_repair /dev/device
xfs_repair
utility is highly scalable and is designed to repair even very large file systems with many inodes efficiently. Unlike other Linux file systems, xfs_repair
does not run at boot time, even when an XFS file system was not cleanly unmounted. In the event of an unclean unmount, xfs_repair
simply replays the log at mount time, ensuring a consistent file system.
Warning
xfs_repair
utility cannot repair an XFS file system with a dirty log. To clear the log, mount and unmount the XFS file system. If the log is corrupt and cannot be replayed, use the -L
option ("force log zeroing") to clear the log, that is, xfs_repair -L /dev/device
. Be aware that this may result in further corruption or data loss.
man xfs_repair
.
3.6. Suspending an XFS File System
#
xfs_freeze mount-point
Note
xfs_freeze
utility is provided by the xfsprogs
package, which is only available on x86_64.
#
xfs_freeze -f /mount/point
#
xfs_freeze -u /mount/point
xfs_freeze
to suspend the file system first. Rather, the LVM management tools will automatically suspend the XFS file system before taking the snapshot.
man xfs_freeze
.
3.7. Backing Up and Restoring XFS File Systems
- xfsdump for creating the backup
- xfsrestore for restoring from backup
3.7.1. Features of XFS Backup and Restoration
Backup
xfsdump
utility to:
- Perform backups to regular file images.Only one backup can be written to a regular file.
- Perform backups to tape drives.The
xfsdump
utility also allows you to write multiple backups to the same tape. A backup can span multiple tapes.To back up multiple file systems to a single tape device, simply write the backup to a tape that already contains an XFS backup. This appends the new backup to the previous one. By default,xfsdump
never overwrites existing backups. - Create incremental backups.The
xfsdump
utility uses dump levels to determine a base backup to which other backups are relative. Numbers from0
to9
refer to increasing dump levels. An incremental backup only backs up files that have changed since the last dump of a lower level:- To perform a full backup, perform a level 0 dump on the file system.
- A level 1 dump is the first incremental backup after a full backup. The next incremental backup would be level 2, which only backs up files that have changed since the last level 1 dump; and so on, to a maximum of level 9.
- Exclude files from a backup using size, subtree, or inode flags to filter them.
Restoration
xfsrestore
interactive mode. The interactive mode provides a set of commands to manipulate the backup files.
3.7.2. Backing Up an XFS File System
Procedure 3.1. Backing Up an XFS File System
- Use the following command to back up an XFS file system:
#
xfsdump -l level [-L label] -f backup-destination path-to-xfs-filesystem
- Replace level with the dump level of your backup. Use
0
to perform a full backup or1
to9
to perform consequent incremental backups. - Replace backup-destination with the path where you want to store your backup. The destination can be a regular file, a tape drive, or a remote tape device. For example,
/backup-files/Data.xfsdump
for a file or/dev/st0
for a tape drive. - Replace path-to-xfs-filesystem with the mount point of the XFS file system you want to back up. For example,
/mnt/data/
. The file system must be mounted. - When backing up multiple file systems and saving them on a single tape device, add a session label to each backup using the
-L label
option so that it is easier to identify them when restoring. Replace label with any name for your backup: for example,backup_data
.
Example 3.4. Backing up Multiple XFS File Systems
- To back up the content of XFS file systems mounted on the
/boot/
and/data/
directories and save them as files in the/backup-files/
directory:#
xfsdump -l 0 -f /backup-files/boot.xfsdump /boot
#
xfsdump -l 0 -f /backup-files/data.xfsdump /data
- To back up multiple file systems on a single tape device, add a session label to each backup using the
-L label
option:#
xfsdump -l 0 -L "backup_boot" -f /dev/st0 /boot
#
xfsdump -l 0 -L "backup_data" -f /dev/st0 /data
Additional Resources
- For more information about backing up XFS file systems, see the xfsdump(8) man page.
3.7.3. Restoring an XFS File System from Backup
Prerequisites
- You need a file or tape backup of XFS file systems, as described in Section 3.7.2, “Backing Up an XFS File System”.
Procedure 3.2. Restoring an XFS File System from Backup
- The command to restore the backup varies depending on whether you are restoring from a full backup or an incremental one, or are restoring multiple backups from a single tape device:
#
xfsrestore [-r] [-S session-id] [-L session-label] [-i]
-f backup-location
restoration-path
- Replace backup-location with the location of the backup. This can be a regular file, a tape drive, or a remote tape device. For example,
/backup-files/Data.xfsdump
for a file or/dev/st0
for a tape drive. - Replace restoration-path with the path to the directory where you want to restore the file system. For example,
/mnt/data/
. - To restore a file system from an incremental (level 1 to level 9) backup, add the
-r
option. - To restore a backup from a tape device that contains multiple backups, specify the backup using the
-S
or-L
options.The-S
lets you choose a backup by its session ID, while the-L
lets you choose by the session label. To obtain the session ID and session labels, use thexfsrestore -I
command.Replace session-id with the session ID of the backup. For example,b74a3586-e52e-4a4a-8775-c3334fa8ea2c
. Replace session-label with the session label of the backup. For example,my_backup_session_label
. - To use
xfsrestore
interactively, use the-i
option.The interactive dialog begins afterxfsrestore
finishes reading the specified device. Available commands in the interactivexfsrestore
shell includecd
,ls
,add
,delete
, andextract
; for a complete list of commands, use thehelp
command.
Example 3.5. Restoring Multiple XFS File Systems
/mnt/
:
#
xfsrestore -f /backup-files/boot.xfsdump /mnt/boot/
#
xfsrestore -f /backup-files/data.xfsdump /mnt/data/
#
xfsrestore -f /dev/st0 -L "backup_boot" /mnt/boot/
#
xfsrestore -f /dev/st0 -S "45e9af35-efd2-4244-87bc-4762e476cbab" /mnt/data/
Informational Messages When Restoring a Backup from a Tape
xfsrestore
utility might issue messages. The messages inform you whether a match of the requested backup has been found when xfsrestore
examines each backup on the tape in sequential order. For example:
xfsrestore: preparing drive xfsrestore: examining media file 0 xfsrestore: inventory session uuid (8590224e-3c93-469c-a311-fc8f23029b2a) does not match the media header's session uuid (7eda9f86-f1e9-4dfd-b1d4-c50467912408) xfsrestore: examining media file 1 xfsrestore: inventory session uuid (8590224e-3c93-469c-a311-fc8f23029b2a) does not match the media header's session uuid (7eda9f86-f1e9-4dfd-b1d4-c50467912408) [...]
Additional Resources
- For more information about restoring XFS file systems, see the xfsrestore(8) man page.
3.8. Configuring Error Behavior
- Continue retries until either:
- the I/O operation succeeds, or
- an I/O operation retry count or time limit is exceeded.
- Consider the error permanent and halt the system.
EIO
: Error while trying to write to the deviceENOSPC
: No space left on the deviceENODEV
: Device cannot be found
3.8.1. Configuration Files for Specific and Undefined Conditions
/sys/fs/xfs/device/error/
directory.
/sys/fs/xfs/device/error/metadata/
directory contains subdirectories for each specific error condition:
/sys/fs/xfs/device/error/metadata/EIO/
for theEIO
error condition/sys/fs/xfs/device/error/metadata/ENODEV/
for theENODEV
error condition/sys/fs/xfs/device/error/metadata/ENOSPC/
for theENOSPC
error condition
/sys/fs/xfs/device/error/metadata/condition/max_retries
: controls the maximum number of times that XFS retries the operation./sys/fs/xfs/device/error/metadata/condition/retry_timeout_seconds
: the time limit in seconds after which XFS will stop retrying the operation
/sys/fs/xfs/device/error/metadata/default/max_retries
: controls the maximum number of retries/sys/fs/xfs/device/error/metadata/default/retry_timeout_seconds
: controls the time limit for retrying
3.8.2. Setting File System Behavior for Specific and Undefined Conditions
max_retries
file.
- For specific conditions:
#
echo value > /sys/fs/xfs/device/error/metadata/condition/max_retries
- For undefined conditions:
#
echo value > /sys/fs/xfs/device/error/metadata/default/max_retries
-1
and the maximum possible value of int
, the C signed integer type. This is 2147483647
on 64-bit Linux.
retry_timeout_seconds
file.
- For specific conditions:
#
echo value > /sys/fs/xfs/device/error/metadata/condition/retry_timeout_seconds
- For undefined conditions:
#
echo value > /sys/fs/xfs/device/error/metadata/default/retry_timeout_seconds
-1
and 86400
, which is the number of seconds in a day.
max_retries
and retry_timeout_seconds
options, -1
means to retry forever and 0
to stop immediately.
/dev/
directory; for example, sda
.
Note
ENODEV
, are considered to be fatal and unrecoverable, regardless of the retry count, so their default value is 0
.
3.8.3. Setting Unmount Behavior
fail_at_unmount
option is set, the file system overrides all other error configurations during unmount, and immediately umnounts the file system without retrying the I/O operation. This allows the unmount operation to succeed even in case of persistent errors.
#
echo value > /sys/fs/xfs/device/error/fail_at_unmount
1
or 0
:
1
means to cancel retrying immediately if an error is found.0
means to respect themax_retries
andretry_timeout_seconds
options.
/dev/
directory; for example, sda
.
Important
fail_at_unmount
option has to be set as desired before attempting to unmount the file system. After an unmount operation has started, the configuration files and directories may be unavailable.
3.9. Other XFS File System Utilities
- xfs_fsr
- Used to defragment mounted XFS file systems. When invoked with no arguments,
xfs_fsr
defragments all regular files in all mounted XFS file systems. This utility also allows users to suspend a defragmentation at a specified time and resume from where it left off later.In addition,xfs_fsr
also allows the defragmentation of only one file, as inxfs_fsr /path/to/file
. Red Hat advises not to periodically defrag an entire file system because XFS avoids fragmentation by default. System wide defragmentation could cause the side effect of fragmentation in free space. - xfs_bmap
- Prints the map of disk blocks used by files in an XFS filesystem. This map lists each extent used by a specified file, as well as regions in the file with no corresponding blocks (that is, holes).
- xfs_info
- Prints XFS file system information.
- xfs_admin
- Changes the parameters of an XFS file system. The
xfs_admin
utility can only modify parameters of unmounted devices or file systems. - xfs_copy
- Copies the contents of an entire XFS file system to one or more targets in parallel.
- xfs_metadump
- Copies XFS file system metadata to a file. Red Hat only supports using the
xfs_metadump
utility to copy unmounted file systems or read-only mounted file systems; otherwise, generated dumps could be corrupted or inconsistent. - xfs_mdrestore
- Restores an XFS metadump image (generated using
xfs_metadump
) to a file system image. - xfs_db
- Debugs an XFS file system.
man
pages.
3.10. Migrating from ext4 to XFS
3.10.1. Differences Between Ext3/4 and XFS
- File system repair
- Ext3/4 runs
e2fsck
in userspace at boot time to recover the journal as needed. XFS, by comparison, performs journal recovery in kernelspace at mount time. Anfsck.xfs
shell script is provided but does not perform any useful action as it is only there to satisfy initscript requirements.When an XFS file system repair or check is requested, use thexfs_repair
command. Use the-n
option for a read-only check.Thexfs_repair
command will not operate on a file system with a dirty log. To repair such a file systemmount
andunmount
must first be performed to replay the log. If the log is corrupt and cannot be replayed, the-L
option can be used to zero out in the log.For more information on file system repair of XFS file systems, see Section 12.2.2, “XFS” - Metadata error behavior
- The ext3/4 file system has configurable behavior when metadata errors are encountered, with the default being to simply continue. When XFS encounters a metadata error that is not recoverable it will shut down the file system and return a
EFSCORRUPTED
error. The system logs will contain details of the error encountered and will recommend runningxfs_repair
if necessary. - Quotas
- XFS quotas are not a remountable option. The
-o quota
option must be specified on the initial mount for quotas to be in effect.While the standard tools in the quota package can perform basic quota administrative tasks (tools such as setquota and repquota), the xfs_quota tool can be used for XFS-specific features, such as Project Quota administration.Thequotacheck
command has no effect on an XFS file system. The first time quota accounting is turned on XFS does an automaticquotacheck
internally. Because XFS quota metadata is a first-class, journaled metadata object, the quota system will always be consistent until quotas are manually turned off. - File system resize
- The XFS file system has no utility to shrink a file system. XFS file systems can be grown online via the
xfs_growfs
command. - Inode numbers
- For file systems larger than 1 TB with 256-byte inodes, or larger than 2 TB with 512-byte inodes, XFS inode numbers might exceed 2^32. Such large inode numbers cause 32-bit stat calls to fail with the EOVERFLOW return value. The described problem might occur when using the default Red Hat Enterprise Linux 7 configuration: non-striped with four allocation groups. A custom configuration, for example file system extension or changing XFS file system parameters, might lead to a different behavior.Applications usually handle such larger inode numbers correctly. If needed, mount the XFS file system with the
-o inode32
parameter to enforce inode numbers below 2^32. Note that usinginode32
does not affect inodes that are already allocated with 64-bit numbers.Important
Do not use theinode32
option unless it is required by a specific environment. Theinode32
option changes allocation behavior. As a consequence, the ENOSPC error might occur if no space is available to allocate inodes in the lower disk blocks. - Speculative preallocation
- XFS uses speculative preallocation to allocate blocks past EOF as files are written. This avoids file fragmentation due to concurrent streaming write workloads on NFS servers. By default, this preallocation increases with the size of the file and will be apparent in "du" output. If a file with speculative preallocation is not dirtied for five minutes the preallocation will be discarded. If the inode is cycled out of cache before that time, then the preallocation will be discarded when the inode is reclaimed.If premature ENOSPC problems are seen due to speculative preallocation, a fixed preallocation amount may be specified with the
-o allocsize=amount
mount option. - Fragmentation-related tools
- Fragmentation is rarely a significant issue on XFS file systems due to heuristics and behaviors, such as delayed allocation and speculative preallocation. However, tools exist for measuring file system fragmentation as well as defragmenting file systems. Their use is not encouraged.The
xfs_db frag
command attempts to distill all file system allocations into a single fragmentation number, expressed as a percentage. The output of the command requires significant expertise to understand its meaning. For example, a fragmentation factor of 75% means only an average of 4 extents per file. For this reason the output of xfs_db's frag is not considered useful and more careful analysis of any fragmentation problems is recommended.Warning
Thexfs_fsr
command may be used to defragment individual files, or all files on a file system. The later is especially not recommended as it may destroy locality of files and may fragment free space.
Commands Used with ext3 and ext4 Compared to XFS
Task | ext3/4 | XFS |
---|---|---|
Create a file system | mkfs.ext4 or mkfs.ext3 | mkfs.xfs |
File system check | e2fsck | xfs_repair |
Resizing a file system | resize2fs | xfs_growfs |
Save an image of a file system | e2image | xfs_metadump and xfs_mdrestore |
Label or tune a file system | tune2fs | xfs_admin |
Backup a file system | dump and restore | xfsdump and xfsrestore |
Task | ext4 | XFS |
---|---|---|
Quota | quota | xfs_quota |
File mapping | filefrag | xfs_bmap |
Chapter 4. The ext3 File System
- Availability
- After an unexpected power failure or system crash (also called an unclean system shutdown), each mounted ext2 file system on the machine must be checked for consistency by the
e2fsck
program. This is a time-consuming process that can delay system boot time significantly, especially with large volumes containing a large number of files. During this time, any data on the volumes is unreachable.It is possible to runfsck -n
on a live filesystem. However, it will not make any changes and may give misleading results if partially written metadata is encountered.If LVM is used in the stack, another option is to take an LVM snapshot of the filesystem and runfsck
on it instead.Finally, there is the option to remount the filesystem as read only. All pending metadata updates (and writes) are then forced to the disk prior to the remount. This ensures the filesystem is in a consistent state, provided there is no previous corruption. It is now possible to runfsck -n
.The journaling provided by the ext3 file system means that this sort of file system check is no longer necessary after an unclean system shutdown. The only time a consistency check occurs using ext3 is in certain rare hardware failure cases, such as hard drive failures. The time to recover an ext3 file system after an unclean system shutdown does not depend on the size of the file system or the number of files; rather, it depends on the size of the journal used to maintain consistency. The default journal size takes about a second to recover, depending on the speed of the hardware.Note
The only journaling mode in ext3 supported by Red Hat isdata=ordered
(default). - Data Integrity
- The ext3 file system prevents loss of data integrity in the event that an unclean system shutdown occurs. The ext3 file system allows you to choose the type and level of protection that your data receives. With regard to the state of the file system, ext3 volumes are configured to keep a high level of data consistency by default.
- Speed
- Despite writing some data more than once, ext3 has a higher throughput in most cases than ext2 because ext3's journaling optimizes hard drive head motion. You can choose from three journaling modes to optimize speed, but doing so means trade-offs in regards to data integrity if the system was to fail.
Note
The only journaling mode in ext3 supported by Red Hat isdata=ordered
(default). - Easy Transition
- It is easy to migrate from ext2 to ext3 and gain the benefits of a robust journaling file system without reformatting. For more information on performing this task, see Section 4.2, “Converting to an ext3 File System” .
Note
ext4.ko
for these on-disk formats. This means that kernel messages will always refer to ext4 regardless of the ext file system used.
4.1. Creating an ext3 File System
- Format the partition or LVM volume with the ext3 file system using the
mkfs.ext3
utility:#
mkfs.ext3 block_device
- Replace block_device with the path to a block device. For example,
/dev/sdb1
,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a
, or/dev/my-volgroup/my-lv
.
- Label the file system using the
e2label
utility:#
e2label block_device volume_label
Configuring UUID
-U
option:
#
mkfs.ext3 -U UUID device
- Replace UUID with the UUID you want to set: for example,
7cd65de3-e0be-41d9-b66d-96d749c02da7
. - Replace device with the path to an ext3 file system to have the UUID added to it: for example,
/dev/sda8
.
Additional Resources
- The mkfs.ext3(8) man page
- The e2label(8) man page
4.2. Converting to an ext3 File System
tune2fs
command converts an ext2
file system to ext3
.
Note
e2fsck
utility to check your file system before and after using tune2fs
. Before trying to convert ext2 to ext3, back up all file systems in case any errors occur.
ext2
file system to ext3
, log in as root and type the following command in a terminal:
# tune2fs -j block_device
df
command to display mounted file systems.
4.3. Reverting to an Ext2 File System
/dev/mapper/VolGroup00-LogVol02
Procedure 4.1. Revert from ext3 to ext2
- Unmount the partition by logging in as root and typing:
# umount /dev/mapper/VolGroup00-LogVol02
- Change the file system type to ext2 by typing the following command:
# tune2fs -O ^has_journal /dev/mapper/VolGroup00-LogVol02
- Check the partition for errors by typing the following command:
# e2fsck -y /dev/mapper/VolGroup00-LogVol02
- Then mount the partition again as ext2 file system by typing:
# mount -t ext2 /dev/mapper/VolGroup00-LogVol02 /mount/point
Replace /mount/point with the mount point of the partition.Note
If a.journal
file exists at the root level of the partition, delete it.
/etc/fstab
file, otherwise it will revert back after booting.
Chapter 5. The ext4 File System
Note
fsck
. For more information, see Chapter 4, The ext3 File System.
- Main Features
- The ext4 file system uses extents (as opposed to the traditional block mapping scheme used by ext2 and ext3), which improves performance when using large files and reduces metadata overhead for large files. In addition, ext4 also labels unallocated block groups and inode table sections accordingly, which allows them to be skipped during a file system check. This makes for quicker file system checks, which becomes more beneficial as the file system grows in size.
- Allocation Features
- The ext4 file system features the following allocation schemes:
- Persistent pre-allocation
- Delayed allocation
- Multi-block allocation
- Stripe-aware allocation
Because of delayed allocation and other performance optimizations, ext4's behavior of writing files to disk is different from ext3. In ext4, when a program writes to the file system, it is not guaranteed to be on-disk unless the program issues anfsync()
call afterwards.By default, ext3 automatically forces newly created files to disk almost immediately even withoutfsync()
. This behavior hid bugs in programs that did not usefsync()
to ensure that written data was on-disk. The ext4 file system, on the other hand, often waits several seconds to write out changes to disk, allowing it to combine and reorder writes for better disk performance than ext3.Warning
Unlike ext3, the ext4 file system does not force data to disk on transaction commit. As such, it takes longer for buffered writes to be flushed to disk. As with any file system, use data integrity calls such asfsync()
to ensure that data is written to permanent storage. - Other ext4 Features
- The ext4 file system also supports the following:
- Extended attributes (
xattr
) — This allows the system to associate several additional name and value pairs per file. - Quota journaling — This avoids the need for lengthy quota consistency checks after a crash.
Note
The only supported journaling mode in ext4 isdata=ordered
(default). - Subsecond timestamps — This gives timestamps to the subsecond.
5.1. Creating an ext4 File System
- To create an ext4 file system, use the following command:
#
mkfs.ext4 block_device
- Replace block_device with the path to a block device. For example,
/dev/sdb1
,/dev/disk/by-uuid/05e99ec8-def1-4a5e-8a9d-5945339ceb2a
, or/dev/my-volgroup/my-lv
. - In general, the default options are optimal for most usage scenarios.
Example 5.1. mkfs.ext4
Command Output
~]#
mkfs.ext4 /dev/sdb1
mke2fs 1.41.12 (17-May-2010) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 245280 inodes, 979456 blocks 48972 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=1006632960 30 block groups 32768 blocks per group, 32768 fragments per group 8176 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736 Writing inode tables: done Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: done
Important
tune2fs
to enable certain ext4 features on ext3 file systems. However, using tune2fs
in this way has not been fully tested and is therefore not supported in Red Hat Enterprise Linux 7. As a result, Red Hat cannot guarantee consistent performance and predictable behavior for ext3 file systems converted or mounted by using tune2fs
.
Striped Block Devices
mkfs.ext4
chooses an optimal geometry. This may also be true on some hardware RAIDs which export geometry information to the operating system.
-E
option of mkfs.ext4
(that is, extended file system options) with the following sub-options:
- stride=value
- Specifies the RAID chunk size.
- stripe-width=value
- Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
value
must be specified in file system block units. For example, to create a file system with a 64k stride (that is, 16 x 4096) on a 4k-block file system, use the following command:
#
mkfs.ext4 -E stride=16,stripe-width=64 /dev/block_device
Configuring UUID
-U
option:
#
mkfs.ext4 -U UUID device
- Replace UUID with the UUID you want to set: for example,
7cd65de3-e0be-41d9-b66d-96d749c02da7
. - Replace device with the path to an ext4 file system to have the UUID added to it: for example,
/dev/sda8
.
Additional Resources
- The mkfs.ext4(8) man page
5.2. Mounting an ext4 File System
#
mount /dev/device /mount/point
acl
parameter enables access control lists, while the user_xattr
parameter enables user extended attributes. To enable both options, use their respective parameters with -o
, as in:
#
mount -o acl,user_xattr /dev/device /mount/point
data_err=abort
can be used to abort the journal if an error occurs in file data.
#
mount -o data_err=abort /dev/device /mount/point
tune2fs
utility also allows administrators to set default mount options in the file system superblock. For more information on this, refer to man tune2fs
.
Write Barriers
nobarrier
option, as in:
#
mount -o nobarrier /dev/device /mount/point
Direct Access Technology Preview
Direct Access
(DAX) provides, as a Technology Preview on the ext4 and XFS file systems, a means for an application to directly map persistent memory into its address space. To use DAX, a system must have some form of persistent memory available, usually in the form of one or more Non-Volatile Dual In-line Memory Modules (NVDIMMs), and a file system that supports DAX must be created on the NVDIMM(s). Also, the file system must be mounted with the dax
mount option. Then, an mmap
of a file on the dax-mounted file system results in a direct mapping of storage into the application's address space.
5.3. Resizing an ext4 File System
resize2fs
command:
#
resize2fs /mount/device size
resize2fs
command can also decrease the size of an unmounted ext4 file system:
#
resize2fs /dev/device size
resize2fs
utility reads the size in units of file system block size, unless a suffix indicating a specific unit is used. The following suffixes indicate specific units:
s
— 512 byte sectorsK
— kilobytesM
— megabytesG
— gigabytes
Note
resize2fs
automatically expands to fill all available space of the container, usually a logical volume or partition.
man resize2fs
.
5.4. Backing up ext2, ext3, or ext4 File Systems
Prerequisites
- If the system has been running for a long time, run the
e2fsck
utility on the partitions before backup:#
e2fsck /dev/device
Procedure 5.1. Backing up ext2, ext3, or ext4 File Systems
- Back up configuration information, including the content of the
/etc/fstab
file and the output of thefdisk -l
command. This is useful for restoring the partitions.To capture this information, run thesosreport
orsysreport
utilities. For more information aboutsosreport
, see the What is a sosreport and how to create one in Red Hat Enterprise Linux 4.6 and later? Kdowledgebase article. - Depending on the role of the partition:
- If the partition you are backing up is an operating system partition, boot your system into the rescue mode. See the Booting to Rescue Mode section of the System Administrator's Guide.
- When backing up a regular, data partition, unmount it.Although it is possible to back up a data partition while it is mounted, the results of backing up a mounted data partition can be unpredictable.If you need to back up a mounted file system using the
dump
utility, do so when the file system is not under a heavy load. The more activity is happening on the file system when backing up, the higher the risk of backup corruption is.
- Use the
dump
utility to back up the content of the partitions:#
dump -0uf backup-file /dev/device
Replace backup-file with a path to a file where you want the to store the backup. Replace device with the name of the ext4 partition you want to back up. Make sure that you are saving the backup to a directory mounted on a different partition than the partition you are backing up.Example 5.2. Backing up Multiple ext4 Partitions
To back up the content of the/dev/sda1
,/dev/sda2
, and/dev/sda3
partitions into backup files stored in the/backup-files/
directory, use the following commands:#
dump -0uf /backup-files/sda1.dump /dev/sda1
#
dump -0uf /backup-files/sda2.dump /dev/sda2
#
dump -0uf /backup-files/sda3.dump /dev/sda3
To do a remote backup, use thessh
utility or configure a password-lessssh
login. For more information onssh
and password-less login, see the Using the ssh Utility and Using Key-based Authentication sections of the System Administrator's Guide.For example, when usingssh
:Example 5.3. Performing a Remote Backup Using
ssh
#
dump -0u -f - /dev/device | ssh root@remoteserver.example.com dd of=backup-file
Note that if using standard redirection, you must pass the-f
option separately.
Additional Resources
- For more information, see the dump(8) man page.
5.5. Restoring ext2, ext3, or ext4 File Systems
Prerequisites
- You need a backup of partitions and their metadata, as described in Section 5.4, “Backing up ext2, ext3, or ext4 File Systems”.
Procedure 5.2. Restoring ext2, ext3, or ext4 File Systems
- If you are restoring an operating system partition, boot your system into Rescue Mode. See the Booting to Rescue Mode section of the System Administrator's Guide.This step is not required for ordinary data partitions.
- Rebuild the partitions you want to restore by using the
fdisk
orparted
utilites.If the partitions no longer exist, recreate them. The new partitions must be large enough to contain the restored data. It is important to get the start and end numbers right; these are the starting and ending sector numbers of the partitions obtained from thefdisk
utility when backing up.For more information on modifying partitions, see Chapter 13, Partitions - Use the
mkfs
utility to format the destination partition:#
mkfs.ext4 /dev/device
Important
Do not format the partition that stores your backup files. - If you created new partitions, re-label all the partitions so they match their entries in the
/etc/fstab
file:#
e2label /dev/device label
- Create temporary mount points and mount the partitions on them:
#
mkdir /mnt/device
#
mount -t ext4 /dev/device /mnt/device
- Restore the data from backup on the mounted partition:
#
cd /mnt/device
#
restore -rf device-backup-file
If you want to restore on a remote machine or restore from a backup file that is stored on a remote host, you can use thessh
utility. For more information onssh
, see the Using the ssh Utility section of the System Administrator's Guide.Note that you need to configure a password-less login for the following commands. For more information on setting up a password-lessssh
login, see the Using Key-based Authentication section of the System Administrator's Guide.- To restore a partition on a remote machine from a backup file stored on the same machine:
#
ssh remote-address "cd /mnt/device && cat backup-file | /usr/sbin/restore -r -f -"
- To restore a partition on a remote machine from a backup file stored on a different remote machine:
#
ssh remote-machine-1 "cd /mnt/device && RSH=/usr/bin/ssh /usr/sbin/restore -rf remote-machine-2:backup-file"
- Reboot:
#
systemctl reboot
Example 5.4. Restoring Multiple ext4 Partitions
/dev/sda1
, /dev/sda2
, and /dev/sda3
partitions from Example 5.2, “Backing up Multiple ext4 Partitions”:
- Rebuild partitions you want to restore by using the
fdisk
command. - Format the destination partitions:
#
mkfs.ext4 /dev/sda1
#
mkfs.ext4 /dev/sda2
#
mkfs.ext4 /dev/sda3
- Re-label all the partitions so they match the
/etc/fstab
file:#
e2label /dev/sda1 Boot1
#
e2label /dev/sda2 Root
#
e2label /dev/sda3 Data
- Prepare the working directories.Mount the new partitions:
#
mkdir /mnt/sda1
#
mount -t ext4 /dev/sda1 /mnt/sda1
#
mkdir /mnt/sda2
#
mount -t ext4 /dev/sda2 /mnt/sda2
#
mkdir /mnt/sda3
#
mount -t ext4 /dev/sda3 /mnt/sda3
Mount the partition that contains backup files:#
mkdir /backup-files
#
mount -t ext4 /dev/sda6 /backup-files
- Restore the data from backup to the mounted partitions:
#
cd /mnt/sda1
#
restore -rf /backup-files/sda1.dump
#
cd /mnt/sda2
#
restore -rf /backup-files/sda2.dump
#
cd /mnt/sda3
#
restore -rf /backup-files/sda3.dump
- Reboot:
#
systemctl reboot
Additional Resources
- For more information, see the restore(8) man page.
5.6. Other ext4 File System Utilities
- e2fsck
- Used to repair an ext4 file system. This tool checks and repairs an ext4 file system more efficiently than ext3, thanks to updates in the ext4 disk structure.
- e2label
- Changes the label on an ext4 file system. This tool also works on ext2 and ext3 file systems.
- quota
- Controls and reports on disk space (blocks) and file (inode) usage by users and groups on an ext4 file system. For more information on using
quota
, refer toman quota
and Section 17.1, “Configuring Disk Quotas”. - fsfreeze
- To suspend access to a file system, use the command
# fsfreeze -f mount-point
to freeze it and# fsfreeze -u mount-point
to unfreeze it. This halts access to the file system and creates a stable image on disk.Note
It is unnecessary to usefsfreeze
for device-mapper drives.For more information see thefsfreeze(8)
manpage.
tune2fs
utility can also adjust configurable file system parameters for ext2, ext3, and ext4 file systems. In addition, the following tools are also useful in debugging and analyzing ext4 file systems:
- debugfs
- Debugs ext2, ext3, or ext4 file systems.
- e2image
- Saves critical ext2, ext3, or ext4 file system metadata to a file.
man
pages.
Chapter 6. Btrfs (Technology Preview)
Note
6.1. Creating a btrfs File System
# mkfs.btrfs /dev/device
6.2. Mounting a btrfs file system
# mount /dev/device /mount-point
- device=/dev/name
- Appending this option to the mount command tells btrfs to scan the named device for a btrfs volume. This is used to ensure the mount will succeed as attempting to mount devices that are not btrfs will cause the mount to fail.
Note
This does not mean all devices will be added to the file system, it only scans them. - max_inline=number
- Use this option to set the maximum amount of space (in bytes) that can be used to inline data within a metadata B-tree leaf. The default is 8192 bytes. For 4k pages it is limited to 3900 bytes due to additional headers that need to fit into the leaf.
- alloc_start=number
- Use this option to set where in the disk allocations start.
- thread_pool=number
- Use this option to assign the number of worker threads allocated.
- discard
- Use this option to enable discard/TRIM on freed blocks.
- noacl
- Use this option to disable the use of ACL's.
- space_cache
- Use this option to store the free space data on disk to make caching a block group faster. This is a persistent change and is safe to boot into old kernels.
- nospace_cache
- Use this option to disable the above
space_cache
. - clear_cache
- Use this option to clear all the free space caches during mount. This is a safe option but will trigger the space cache to be rebuilt. As such, leave the file system mounted in order to let the rebuild process finish. This mount option is intended to be used once and only after problems are apparent with the free space.
- enospc_debug
- This option is used to debug problems with "no space left".
- recovery
- Use this option to enable autorecovery upon mount.
6.3. Resizing a btrfs File System
Note
G
or g
for GiB.
t
for terabytes or p
for petabytes. It only accepts k
, m
, and g
.
Enlarging a btrfs File System
# btrfs filesystem resize amount /mount-point
# btrfs filesystem resize +200M /btrfssingle Resize '/btrfssingle' of '+200M'
# btrfs filesystem show /mount-point
# btrfs filesystem show /btrfstest Label: none uuid: 755b41b7-7a20-4a24-abb3-45fdbed1ab39 Total devices 4 FS bytes used 192.00KiB devid 1 size 1.00GiB used 224.75MiB path /dev/vdc devid 2 size 524.00MiB used 204.75MiB path /dev/vdd devid 3 size 1.00GiB used 8.00MiB path /dev/vde devid 4 size 1.00GiB used 8.00MiB path /dev/vdf Btrfs v3.16.2
devid
of the device to be enlarged, use the following command:
# btrfs filesystem resize devid:amount /mount-point
# btrfs filesystem resize 2:+200M /btrfstest Resize '/btrfstest/' of '2:+200M'
Note
max
instead of a specified amount. This will use all remaining free space on the device.
Shrinking a btrfs File System
# btrfs filesystem resize amount /mount-point
# btrfs filesystem resize -200M /btrfssingle Resize '/btrfssingle' of '-200M'
# btrfs filesystem show /mount-point
# btrfs filesystem show /btrfstest Label: none uuid: 755b41b7-7a20-4a24-abb3-45fdbed1ab39 Total devices 4 FS bytes used 192.00KiB devid 1 size 1.00GiB used 224.75MiB path /dev/vdc devid 2 size 524.00MiB used 204.75MiB path /dev/vdd devid 3 size 1.00GiB used 8.00MiB path /dev/vde devid 4 size 1.00GiB used 8.00MiB path /dev/vdf Btrfs v3.16.2
devid
of the device to be shrunk, use the following command:
# btrfs filesystem resize devid:amount /mount-point
# btrfs filesystem resize 2:-200M /btrfstest Resize '/btrfstest' of '2:-200M'
Set the File System Size
# btrfs filesystem resize amount /mount-point
# btrfs filesystem resize 700M /btrfssingle Resize '/btrfssingle' of '700M'
# btrfs filesystem show /mount-point
# btrfs filesystem show /btrfstest Label: none uuid: 755b41b7-7a20-4a24-abb3-45fdbed1ab39 Total devices 4 FS bytes used 192.00KiB devid 1 size 1.00GiB used 224.75MiB path /dev/vdc devid 2 size 724.00MiB used 204.75MiB path /dev/vdd devid 3 size 1.00GiB used 8.00MiB path /dev/vde devid 4 size 1.00GiB used 8.00MiB path /dev/vdf Btrfs v3.16.2
devid
of the device to be changed, use the following command:
# btrfs filesystem resize devid:amount /mount-point
# btrfs filesystem resize 2:300M /btrfstest Resize '/btrfstest' of '2:300M'
6.4. Integrated Volume Management of Multiple Devices
6.4.1. Creating a File System with Multiple Devices
mkfs.btrfs
command, as detailed in Section 6.1, “Creating a btrfs File System”, accepts the options -d
for data, and -m
for metadata. Valid specifications are:
raid0
raid1
raid10
dup
single
-m single
option instructs that no duplication of metadata is done. This may be desired when using hardware raid.
Note
Example 6.1. Creating a RAID 10 btrfs File System
# mkfs.btrfs /dev/device1 /dev/device2 /dev/device3 /dev/device4
# mkfs.btrfs -m raid0 /dev/device1 /dev/device2
# mkfs.btrfs -m raid10 -d raid10 /dev/device1 /dev/device2 /dev/device3 /dev/device4
# mkfs.btrfs -m single /dev/device
single
option to use the full capacity of each drive when the drives are different sizes.
# mkfs.btrfs -d single /dev/device1 /dev/device2 /dev/device3
# btrfs device add /dev/device1 /mount-point
btrfs device scan
command to discover all multi-device file systems. See Section 6.4.2, “Scanning for btrfs Devices” for more information.
6.4.2. Scanning for btrfs Devices
btrfs device scan
to scan all block devices under /dev
and probe for btrfs volumes. This must be performed after loading the btrfs module if running with more than one device in a file system.
# btrfs device scan
# btrfs device scan /dev/device
6.4.3. Adding New Devices to a btrfs File System
btrfs filesystem show
command to list all the btrfs file systems and which devices they include.
btrfs device add
command is used to add new devices to a mounted file system.
btrfs filesystem balance
command balances (restripes) the allocated extents across all existing devices.
Example 6.2. Add a New Device to a btrfs File System
# mkfs.btrfs /dev/device1 # mount /dev/device1
# btrfs device add /dev/device2 /mount-point
/dev/device1
. It must now be balanced to spread across all devices.
# btrfs filesystem balance /mount-point
6.4.4. Converting a btrfs File System
Example 6.3. Converting a btrfs File System
/dev/sdb1
in this case, into a two device, raid1 system in order to protect against a single disk failure, use the following commands:
# mount /dev/sdb1 /mnt # btrfs device add /dev/sdc1 /mnt # btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt
Important
6.4.5. Removing btrfs Devices
btrfs device delete
command to remove an online device. It redistributes any extents in use to other devices in the file system in order to be safely removed.
Example 6.4. Removing a Device on a btrfs File System
# mkfs.btrfs /dev/sdb /dev/sdc /dev/sdd /dev/sde # mount /dev/sdb /mnt
# btrfs device delete /dev/sdc /mnt
6.4.6. Replacing Failed Devices on a btrfs File System
# mkfs.btrfs -m raid1 /dev/sdb /dev/sdc /dev/sdd /dev/sde ssd is destroyed or removed, use -o degraded to force the mount to ignore missing devices # mount -o degraded /dev/sdb /mnt 'missing' is a special device name # btrfs device delete missing /mnt
btrfs device delete missing
removes the first device that is described by the file system metadata but not present when the file system was mounted.
Important
- mount in degraded mode,
- add a new device,
- and, remove the missing device.
6.4.7. Registering a btrfs File System in /etc/fstab
initrd
or it does not perform a btrfs device scan, it is possible to mount a multi-volume btrfs
file system by passing all the devices in the file system explicitly to the mount
command.
Example 6.5. Example /etc/fstab
Entry
/etc/fstab
entry would be:
/dev/sdb /mnt btrfs device=/dev/sdb,device=/dev/sdc,device=/dev/sdd,device=/dev/sde 0
6.5. SSD Optimization
mkfs.btrfs
turns off metadata duplication on a single device when /sys/block/device/queue/rotational
is zero for the single specified device. This is equivalent to specifying -m single
on the command line. It can be overridden and duplicate metadata forced by providing the -m dup
option. Duplication is not required due to SSD firmware potentially losing both copies. This wastes space and is a performance cost.
ssd
, nossd
, and ssd_spread
.
ssd
option does several things:
- It allows larger metadata cluster allocation.
- It allocates data more sequentially where possible.
- It disables btree leaf rewriting to match key and block order.
- It commits log fragments without batching multiple processes.
Note
ssd
mount option only enables the ssd option. Use the nossd
option to disable it.
mount -o ssd
will find groupings of blocks where there are several free blocks that might have allocated blocks mixed in. The command mount -o ssd_spread
ensures there are no allocated blocks mixed in. This improves performance on lower end SSDs.
Note
ssd_spread
option enables both the ssd
and the ssd_spread
options. Use the nossd
to disable both these options.
ssd_spread
option is never automatically set if none of the ssd options are provided and any of the devices are non-rotational.
6.6. btrfs References
btrfs(8)
covers all important management commands. In particular this includes:
- All the subvolume commands for managing snapshots.
- The
device
commands for managing devices. - The
scrub
,balance
, anddefragment
commands.
mkfs.btrfs(8)
contains information on creating a btrfs file system including all the options regarding it.
btrfsck(8)
for information regarding fsck
on btrfs systems.
Chapter 7. Global File System 2
fsck
command on a very large file system can take a long time and consume a large amount of memory. Additionally, in the event of a disk or disk-subsystem failure, recovery time is limited by the speed of backup media.
clvmd
, and running in a Red Hat Cluster Suite cluster. The daemon makes it possible to use LVM2 to manage logical volumes across a cluster, allowing all nodes in the cluster to share the logical volumes. For information on the Logical Volume Manager, see Red Hat's Logical Volume Manager Administration guide.
gfs2.ko
kernel module implements the GFS2 file system and is loaded on GFS2 cluster nodes.
Chapter 8. Network File System (NFS)
8.1. Introduction to NFS
- NFS version 3 (NFSv3) supports safe asynchronous writes and is more robust at error handling than the previous NFSv2. It also supports 64-bit file sizes and offsets, allowing clients to access more than 2 GB of file data.
- NFS version 4 (NFSv4) works through firewalls and on the Internet, no longer requires an
rpcbind
service, supports ACLs, and utilizes stateful operations.
- Sparse Files: It verifies space efficiency of a file and allows placeholder to improve storage efficiency. It is a file having one or more holes; holes are unallocated or uninitialized data blocks consisting only of zeroes.
lseek()
operation in NFSv4.2, supportsseek_hole()
andseek_data()
, which allows application to map out the location of holes in the sparse file. - Space Reservation: It permits storage servers to reserve free space, which prohibits servers to run out of space. NFSv4.2 supports
allocate()
operation to reserve space,deallocate()
operation to unreserve space, andfallocate()
operation to preallocate or deallocate space in a file. - Labeled NFS: It enforces data access rights and enables SELinux labels between a client and a server for individual files on an NFS file system.
- Layout Enhancements: NFSv4.2 provides new operation,
layoutstats()
, which the client can use to notify the metadata server about its communication with the layout.
- Enhances performance and security of network, and also includes client-side support for Parallel NFS (pNFS).
- No longer requires a separate TCP connection for callbacks, which allows an NFS server to grant delegations even when it cannot contact the client. For example, when NAT or a firewall interferes.
- It provides exactly once semantics (except for reboot operations), preventing a previous issue whereby certain operations could return an inaccurate result if a reply was lost and the operation was sent twice.
Note
rpcbind
[1], lockd
, and rpc.statd
daemons. The rpc.mountd
daemon is still required on the NFS server to set up the exports, but is not involved in any over-the-wire operations.
Note
'-p'
command line option that can set the port, making firewall configuration easier.
/etc/exports
configuration file to determine whether the client is allowed to access any exported file systems. Once verified, all file and directory operations are available to the user.
Important
rpc.nfsd
process now allow binding to any specified port during system start up. However, this can be error-prone if the port is unavailable, or if it conflicts with another daemon.
8.1.1. Required Services
rpcbind
service. To share or mount NFS file systems, the following services work together depending on which version of NFS is implemented:
Note
portmap
service was used to map RPC program numbers to IP address port number combinations in earlier versions of Red Hat Enterprise Linux. This service is now replaced by rpcbind
in Red Hat Enterprise Linux 7 to enable IPv6 support.
- nfs
systemctl start nfs
starts the NFS server and the appropriate RPC processes to service requests for shared NFS file systems.- nfslock
systemctl start nfs-lock
activates a mandatory service that starts the appropriate RPC processes allowing NFS clients to lock files on the server.- rpcbind
rpcbind
accepts port reservations from local RPC services. These ports are then made available (or advertised) so the corresponding remote RPC services can access them.rpcbind
responds to requests for RPC services and sets up connections to the requested RPC service. This is not used with NFSv4.
- rpc.mountd
- This process is used by an NFS server to process
MOUNT
requests from NFSv3 clients. It checks that the requested NFS share is currently exported by the NFS server, and that the client is allowed to access it. If the mount request is allowed, the rpc.mountd server replies with aSuccess
status and provides theFile-Handle
for this NFS share back to the NFS client. - rpc.nfsd
rpc.nfsd
allows explicit NFS versions and protocols the server advertises to be defined. It works with the Linux kernel to meet the dynamic demands of NFS clients, such as providing server threads each time an NFS client connects. This process corresponds to thenfs
service.- lockd
lockd
is a kernel thread which runs on both clients and servers. It implements the Network Lock Manager (NLM) protocol, which allows NFSv3 clients to lock files on the server. It is started automatically whenever the NFS server is run and whenever an NFS file system is mounted.- rpc.statd
- This process implements the Network Status Monitor (NSM) RPC protocol, which notifies NFS clients when an NFS server is restarted without being gracefully brought down.
rpc.statd
is started automatically by thenfslock
service, and does not require user configuration. This is not used with NFSv4. - rpc.rquotad
- This process provides user quota information for remote users.
rpc.rquotad
is started automatically by thenfs
service and does not require user configuration. - rpc.idmapd
rpc.idmapd
provides NFSv4 client and server upcalls, which map between on-the-wire NFSv4 names (strings in the form ofuser@domain
) and local UIDs and GIDs. Foridmapd
to function with NFSv4, the/etc/idmapd.conf
file must be configured. At a minimum, the "Domain" parameter should be specified, which defines the NFSv4 mapping domain. If the NFSv4 mapping domain is the same as the DNS domain name, this parameter can be skipped. The client and server must agree on the NFSv4 mapping domain for ID mapping to function properly.Note
In Red Hat Enterprise Linux 7, only the NFSv4 server usesrpc.idmapd
. The NFSv4 client uses the keyring-based idmappernfsidmap
.nfsidmap
is a stand-alone program that is called by the kernel on-demand to perform ID mapping; it is not a daemon. If there is a problem withnfsidmap
does the client fall back to usingrpc.idmapd
. More information regardingnfsidmap
can be found on the nfsidmap man page.
8.2. Configuring NFS Client
mount
command mounts NFS shares on the client side. Its format is as follows:
# mount -t nfs -o options server:/remote/export /local/directory
- options
- A comma-delimited list of mount options; for more information on valid NFS mount options, see Section 8.4, “Common NFS Mount Options”.
- server
- The hostname, IP address, or fully qualified domain name of the server exporting the file system you wish to mount
- /remote/export
- The file system or directory being exported from the server, that is, the directory you wish to mount
- /local/directory
- The client location where /remote/export is mounted
mount
options nfsvers
or vers
. By default, mount
uses NFSv4 with mount -t nfs
. If the server does not support NFSv4, the client automatically steps down to a version supported by the server. If the nfsvers
/vers
option is used to pass a particular version not supported by the server, the mount fails. The file system type nfs4 is also available for legacy reasons; this is equivalent to running mount -t nfs -o nfsvers=4 host:/remote/export /local/directory
.
man mount
.
/etc/fstab
file and the autofs
service. For more information, see Section 8.2.1, “Mounting NFS File Systems Using /etc/fstab
” and Section 8.3, “autofs
”.
8.2.1. Mounting NFS File Systems Using /etc/fstab
/etc/fstab
file. The line must state the hostname of the NFS server, the directory on the server being exported, and the directory on the local machine where the NFS share is to be mounted. You must be root to modify the /etc/fstab
file.
Example 8.1. Syntax Example
/etc/fstab
is as follows:
server:/usr/local/pub /pub nfs defaults 0 0
/pub
must exist on the client machine before this command can be executed. After adding this line to /etc/fstab
on the client system, use the command mount /pub
, and the mount point /pub
is mounted from the server.
/etc/fstab
entry to mount an NFS export should contain the following information:
server:/remote/export /local/directory nfs options 0 0
Note
/etc/fstab
is read. Otherwise, the mount fails.
/etc/fstab
, regenerate mount units so that your system registers the new configuration:
#
systemctl daemon-reload
Additional Resources
- For more information about
/etc/fstab
, refer toman fstab
.
8.3. autofs
/etc/fstab
is that, regardless of how infrequently a user accesses the NFS mounted file system, the system must dedicate resources to keep the mounted file system in place. This is not a problem with one or two mounts, but when the system is maintaining mounts to many systems at one time, overall system performance can be affected. An alternative to /etc/fstab
is to use the kernel-based automount
utility. An automounter consists of two components:
- a kernel module that implements a file system, and
- a user-space daemon that performs all of the other functions.
automount
utility can mount and unmount NFS file systems automatically (on-demand mounting), therefore saving system resources. It can be used to mount other file systems including AFS, SMBFS, CIFS, and local file systems.
Important
autofs
uses /etc/auto.master
(master map) as its default primary configuration file. This can be changed to use another supported network source and name using the autofs
configuration (in /etc/sysconfig/autofs
) in conjunction with the Name Service Switch (NSS) mechanism. An instance of the autofs
version 4 daemon was run for each mount point configured in the master map and so it could be run manually from the command line for any given mount point. This is not possible with autofs
version 5, because it uses a single daemon to manage all configured mount points; as such, all automounts must be configured in the master map. This is in line with the usual requirements of other industry standard automounters. Mount point, hostname, exported directory, and options can all be specified in a set of files (or other supported network sources) rather than configuring them manually for each host.
8.3.1. Improvements in autofs Version 5 over Version 4
autofs
version 5 features the following enhancements over version 4:
- Direct map support
- Direct maps in
autofs
provide a mechanism to automatically mount file systems at arbitrary points in the file system hierarchy. A direct map is denoted by a mount point of/-
in the master map. Entries in a direct map contain an absolute path name as a key (instead of the relative path names used in indirect maps). - Lazy mount and unmount support
- Multi-mount map entries describe a hierarchy of mount points under a single key. A good example of this is the
-hosts
map, commonly used for automounting all exports from a host under/net/host
as a multi-mount map entry. When using the-hosts
map, anls
of/net/host
will mount autofs trigger mounts for each export from host. These will then mount and expire them as they are accessed. This can greatly reduce the number of active mounts needed when accessing a server with a large number of exports. - Enhanced LDAP support
- The
autofs
configuration file (/etc/sysconfig/autofs
) provides a mechanism to specify theautofs
schema that a site implements, thus precluding the need to determine this via trial and error in the application itself. In addition, authenticated binds to the LDAP server are now supported, using most mechanisms supported by the common LDAP server implementations. A new configuration file has been added for this support:/etc/autofs_ldap_auth.conf
. The default configuration file is self-documenting, and uses an XML format. - Proper use of the Name Service Switch (
nsswitch
) configuration. - The Name Service Switch configuration file exists to provide a means of determining from where specific configuration data comes. The reason for this configuration is to allow administrators the flexibility of using the back-end database of choice, while maintaining a uniform software interface to access the data. While the version 4 automounter is becoming increasingly better at handling the NSS configuration, it is still not complete. Autofs version 5, on the other hand, is a complete implementation.For more information on the supported syntax of this file, see
man nsswitch.conf
. Not all NSS databases are valid map sources and the parser will reject ones that are invalid. Valid sources are files,yp
,nis
,nisplus
,ldap
, andhesiod
. - Multiple master map entries per autofs mount point
- One thing that is frequently used but not yet mentioned is the handling of multiple master map entries for the direct mount point
/-
. The map keys for each entry are merged and behave as one map.Example 8.2. Multiple Master Map Entries per autofs Mount Point
Following is an example in the connectathon test maps for the direct mounts:/- /tmp/auto_dcthon /- /tmp/auto_test3_direct /- /tmp/auto_test4_direct
8.3.2. Configuring autofs
/etc/auto.master
, also referred to as the master map which may be changed as described in the Section 8.3.1, “Improvements in autofs Version 5 over Version 4”. The master map lists autofs
-controlled mount points on the system, and their corresponding configuration files or network sources known as automount maps. The format of the master map is as follows:
mount-point map-name options
- mount-point
- The
autofs
mount point,/home
, for example. - map-name
- The name of a map source which contains a list of mount points, and the file system location from which those mount points should be mounted.
- options
- If supplied, these applies to all entries in the given map provided they do not themselves have options specified. This behavior is different from
autofs
version 4 where options were cumulative. This has been changed to implement mixed environment compatibility.
Example 8.3. /etc/auto.master
File
/etc/auto.master
file (displayed with cat /etc/auto.master
):
/home /etc/auto.misc
mount-point [options] location
- mount-point
- This refers to the
autofs
mount point. This can be a single directory name for an indirect mount or the full path of the mount point for direct mounts. Each direct and indirect map entry key (mount-point
) may be followed by a space separated list of offset directories (subdirectory names each beginning with a/
) making them what is known as a multi-mount entry. - options
- Whenever supplied, these are the mount options for the map entries that do not specify their own options.
- location
- This refers to the file system location such as a local file system path (preceded with the Sun map format escape character ":" for map names beginning with
/
), an NFS file system or other valid file system location.
/etc/auto.misc
):
payroll -fstype=nfs personnel:/dev/hda3 sales -fstype=ext3 :/dev/hda4
autofs
mount point (sales
and payroll
from the server called personnel
). The second column indicates the options for the autofs
mount while the third column indicates the source of the mount. Following the given configuration, the autofs mount points will be /home/payroll
and /home/sales
. The -fstype=
option is often omitted and is generally not needed for correct operation.
#
systemctl start autofs
#
systemctl restart autofs
autofs
unmounted directory such as /home/payroll/2006/July.sxc
, the automount daemon automatically mounts the directory. If a timeout is specified, the directory is automatically unmounted if the directory is not accessed for the timeout period.
#
systemctl status autofs
8.3.3. Overriding or Augmenting Site Configuration Files
- Automounter maps are stored in NIS and the
/etc/nsswitch.conf
file has the following directive:automount: files nis
- The
auto.master
file contains:+auto.master
- The NIS
auto.master
map file contains:/home auto.home
- The NIS
auto.home
map contains:beth fileserver.example.com:/export/home/beth joe fileserver.example.com:/export/home/joe * fileserver.example.com:/export/home/&
- The file map
/etc/auto.home
does not exist.
auto.home
and mount home directories from a different server. In this case, the client needs to use the following /etc/auto.master
map:
/home /etc/auto.home +auto.master
/etc/auto.home
map contains the entry:
* labserver.example.com:/export/home/&
/home
contain the contents of /etc/auto.home
instead of the NIS auto.home
map.
auto.home
map with just a few entries, create an /etc/auto.home
file map, and in it put the new entries. At the end, include the NIS auto.home
map. Then the /etc/auto.home
file map looks similar to:
mydir someserver:/export/mydir +auto.home
auto.home
map conditions, the ls /home
command outputs:
beth joe mydir
autofs
does not include the contents of a file map of the same name as the one it is reading. As such, autofs
moves on to the next map source in the nsswitch
configuration.
8.3.4. Using LDAP to Store Automounter Maps
openldap
package should be installed automatically as a dependency of the automounter
. To configure LDAP access, modify /etc/openldap/ldap.conf
. Ensure that BASE, URI, and schema are set appropriately for your site.
rfc2307bis
. To use this schema it is necessary to set it in the autofs
configuration (/etc/sysconfig/autofs
) by removing the comment characters from the schema definition. For example:
Example 8.4. Setting autofs Configuration
DEFAULT_MAP_OBJECT_CLASS="automountMap" DEFAULT_ENTRY_OBJECT_CLASS="automount" DEFAULT_MAP_ATTRIBUTE="automountMapName" DEFAULT_ENTRY_ATTRIBUTE="automountKey" DEFAULT_VALUE_ATTRIBUTE="automountInformation"
automountKey
replaces the cn
attribute in the rfc2307bis
schema. Following is an example of an LDAP Data Interchange Format (LDIF
) configuration:
Example 8.5. LDF Configuration
# extended LDIF # # LDAPv3 # base <> with scope subtree # filter: (&(objectclass=automountMap)(automountMapName=auto.master)) # requesting: ALL # # auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: top objectClass: automountMap automountMapName: auto.master # extended LDIF # # LDAPv3 # base <automountMapName=auto.master,dc=example,dc=com> with scope subtree # filter: (objectclass=automount) # requesting: ALL # # /home, auto.master, example.com dn: automountMapName=auto.master,dc=example,dc=com objectClass: automount cn: /home automountKey: /home automountInformation: auto.home # extended LDIF # # LDAPv3 # base <> with scope subtree # filter: (&(objectclass=automountMap)(automountMapName=auto.home)) # requesting: ALL # # auto.home, example.com dn: automountMapName=auto.home,dc=example,dc=com objectClass: automountMap automountMapName: auto.home # extended LDIF # # LDAPv3 # base <automountMapName=auto.home,dc=example,dc=com> with scope subtree # filter: (objectclass=automount) # requesting: ALL # # foo, auto.home, example.com dn: automountKey=foo,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: foo automountInformation: filer.example.com:/export/foo # /, auto.home, example.com dn: automountKey=/,automountMapName=auto.home,dc=example,dc=com objectClass: automount automountKey: / automountInformation: filer.example.com:/export/&
8.4. Common NFS Mount Options
mount
commands, /etc/fstab
settings, and autofs
.
- lookupcache=mode
- Specifies how the kernel should manage its cache of directory entries for a given mount point. Valid arguments for mode are
all
,none
, orpos
/positive
. - nfsvers=version
- Specifies which version of the NFS protocol to use, where version is 3 or 4. This is useful for hosts that run multiple NFS servers. If no version is specified, NFS uses the highest version supported by the kernel and
mount
command.The optionvers
is identical tonfsvers
, and is included in this release for compatibility reasons. - noacl
- Turns off all ACL processing. This may be needed when interfacing with older versions of Red Hat Enterprise Linux, Red Hat Linux, or Solaris, since the most recent ACL technology is not compatible with older systems.
- nolock
- Disables file locking. This setting is sometimes required when connecting to very old NFS servers.
- noexec
- Prevents execution of binaries on mounted file systems. This is useful if the system is mounting a non-Linux file system containing incompatible binaries.
- nosuid
- Disables
set-user-identifier
orset-group-identifier
bits. This prevents remote users from gaining higher privileges by running asetuid
program. - port=num
- Specifies the numeric value of the NFS server port. If
num
is0
(the default value), thenmount
queries the remote host'srpcbind
service for the port number to use. If the remote host's NFS daemon is not registered with itsrpcbind
service, the standard NFS port number of TCP 2049 is used instead. - rsize=num and wsize=num
- These options set the maximum number of bytes to be transfered in a single NFS read or write operation.There is no fixed default value for
rsize
andwsize
. By default, NFS uses the largest possible value that both the server and the client support. In Red Hat Enterprise Linux 7, the client and server maximum is 1,048,576 bytes. For more details, see the What are the default and maximum values for rsize and wsize with NFS mounts? KBase article. - sec=flavors
- Security flavors to use for accessing files on the mounted export. The flavors value is a colon-separated list of one or more security flavors.By default, the client attempts to find a security flavor that both the client and the server support. If the server does not support any of the selected flavors, the mount operation fails.
sec=sys
uses local UNIX UIDs and GIDs. These useAUTH_SYS
to authenticate NFS operations.sec=krb5
uses Kerberos V5 instead of local UNIX UIDs and GIDs to authenticate users.sec=krb5i
uses Kerberos V5 for user authentication and performs integrity checking of NFS operations using secure checksums to prevent data tampering.sec=krb5p
uses Kerberos V5 for user authentication, integrity checking, and encrypts NFS traffic to prevent traffic sniffing. This is the most secure setting, but it also involves the most performance overhead. - tcp
- Instructs the NFS mount to use the TCP protocol.
- udp
- Instructs the NFS mount to use the UDP protocol.
man mount
and man nfs
.
8.5. Starting and Stopping the NFS Server
Prerequisites
- For servers that support NFSv2 or NFSv3 connections, the
rpcbind
[1] service must be running. To verify thatrpcbind
is active, use the following command:$
systemctl status rpcbind
To configure an NFSv4-only server, which does not requirerpcbind
, see Section 8.6.7, “Configuring an NFSv4-only Server”. - On Red Hat Enterprise Linux 7.0, if your NFS server exports NFSv3 and is enabled to start at boot, you need to manually start and enable the
nfs-lock
service:#
systemctl start nfs-lock
#
systemctl enable nfs-lock
On Red Hat Enterprise Linux 7.1 and later,nfs-lock
starts automatically if needed, and an attempt to enable it manually fails.
Procedures
- To start an NFS server, use the following command:
#
systemctl start nfs
- To enable NFS to start at boot, use the following command:
#
systemctl enable nfs
- To stop the server, use:
#
systemctl stop nfs
- The
restart
option is a shorthand way of stopping and then starting NFS. This is the most efficient way to make configuration changes take effect after editing the configuration file for NFS. To restart the server type:#
systemctl restart nfs
- After you edit the
/etc/sysconfig/nfs
file, restart the nfs-config service by running the following command for the new values to take effect:#
systemctl restart nfs-config
- The
try-restart
command only startsnfs
if it is currently running. This command is the equivalent ofcondrestart
(conditional restart) in Red Hat init scripts and is useful because it does not start the daemon if NFS is not running.To conditionally restart the server, type:#
systemctl try-restart nfs
- To reload the NFS server configuration file without restarting the service type:
#
systemctl reload nfs
8.6. Configuring the NFS Server
- Manually editing the NFS configuration file, that is,
/etc/exports
, and - Through the command line, that is, by using the command
exportfs
8.6.1. The /etc/exports
Configuration File
/etc/exports
file controls which file systems are exported to remote hosts and specifies options. It follows the following syntax rules:
- Blank lines are ignored.
- To add a comment, start a line with the hash mark (
#
). - You can wrap long lines with a backslash (
\
). - Each exported file system should be on its own individual line.
- Any lists of authorized hosts placed after an exported file system must be separated by space characters.
- Options for each of the hosts must be placed in parentheses directly after the host identifier, without any spaces separating the host and the first parenthesis.
export host(options)
- export
- The directory being exported
- host
- The host or network to which the export is being shared
- options
- The options to be used for host
export host1(options1) host2(options2) host3(options3)
/etc/exports
file only specifies the exported directory and the hosts permitted to access it, as in the following example:
Example 8.6. The /etc/exports
File
/exported/directory bob.example.com
bob.example.com
can mount /exported/directory/
from the NFS server. Because no options are specified in this example, NFS uses default settings.
- ro
- The exported file system is read-only. Remote hosts cannot change the data shared on the file system. To allow hosts to make changes to the file system (that is, read and write), specify the
rw
option. - sync
- The NFS server will not reply to requests before changes made by previous requests are written to disk. To enable asynchronous writes instead, specify the option
async
. - wdelay
- The NFS server will delay writing to the disk if it suspects another write request is imminent. This can improve performance as it reduces the number of times the disk must be accessed by separate write commands, thereby reducing write overhead. To disable this, specify the
no_wdelay
.no_wdelay
is only available if the defaultsync
option is also specified. - root_squash
- This prevents root users connected remotely (as opposed to locally) from having root privileges; instead, the NFS server assigns them the user ID
nfsnobody
. This effectively "squashes" the power of the remote root user to the lowest local user, preventing possible unauthorized writes on the remote server. To disable root squashing, specifyno_root_squash
.
all_squash
. To specify the user and group IDs that the NFS server should assign to remote users from a particular host, use the anonuid
and anongid
options, respectively, as in:
export host(anonuid=uid,anongid=gid)
anonuid
and anongid
options allow you to create a special user and group account for remote NFS users to share.
no_acl
option when exporting the file system.
rw
option is not specified, then the exported file system is shared as read-only. The following is a sample line from /etc/exports
which overrides two default options:
/another/exported/directory 192.168.0.3(rw,async)
192.168.0.3
can mount /another/exported/directory/
read and write and all writes to disk are asynchronous. For more information on exporting options, see man exportfs
.
man exports
.
Important
/etc/exports
file is very precise, particularly in regards to use of the space character. Remember to always separate exported file systems from hosts and hosts from one another with a space character. However, there should be no other space characters in the file except on comment lines.
/home bob.example.com(rw) /home bob.example.com (rw)
bob.example.com
read and write access to the /home
directory. The second line allows users from bob.example.com
to mount the directory as read-only (the default), while the rest of the world can mount it read/write.
8.6.2. The exportfs
Command
/etc/exports
file. When the nfs
service starts, the /usr/sbin/exportfs
command launches and reads this file, passes control to rpc.mountd
(if NFSv3) for the actual mounting process, then to rpc.nfsd
where the file systems are then available to remote users.
/usr/sbin/exportfs
command allows the root user to selectively export or unexport directories without restarting the NFS service. When given the proper options, the /usr/sbin/exportfs
command writes the exported file systems to /var/lib/nfs/xtab
. Since rpc.mountd
refers to the xtab
file when deciding access privileges to a file system, changes to the list of exported file systems take effect immediately.
/usr/sbin/exportfs
:
- -r
- Causes all directories listed in
/etc/exports
to be exported by constructing a new export list in/var/lib/nfs/etab
. This option effectively refreshes the export list with any changes made to/etc/exports
. - -a
- Causes all directories to be exported or unexported, depending on what other options are passed to
/usr/sbin/exportfs
. If no other options are specified,/usr/sbin/exportfs
exports all file systems specified in/etc/exports
. - -o file-systems
- Specifies directories to be exported that are not listed in
/etc/exports
. Replace file-systems with additional file systems to be exported. These file systems must be formatted in the same way they are specified in/etc/exports
. This option is often used to test an exported file system before adding it permanently to the list of file systems to be exported. For more information on/etc/exports
syntax, see Section 8.6.1, “The/etc/exports
Configuration File”. - -i
- Ignores
/etc/exports
; only options given from the command line are used to define exported file systems. - -u
- Unexports all shared directories. The command
/usr/sbin/exportfs -ua
suspends NFS file sharing while keeping all NFS daemons up. To re-enable NFS sharing, useexportfs -r
. - -v
- Verbose operation, where the file systems being exported or unexported are displayed in greater detail when the
exportfs
command is executed.
exportfs
command, it displays a list of currently exported file systems. For more information about the exportfs
command, see man exportfs
.
8.6.2.1. Using exportfs
with NFSv4
RPCNFSDARGS= -N 4
in /etc/sysconfig/nfs
.
8.6.3. Running NFS Behind a Firewall
rpcbind
, which dynamically assigns ports for RPC services and can cause issues for configuring firewall rules. To allow clients to access NFS shares behind a firewall, edit the /etc/sysconfig/nfs
file to set which ports the RPC services run on. To allow clients to access RPC Quota through a firewall, see Section 8.6.4, “Accessing RPC Quota through a Firewall”.
/etc/sysconfig/nfs
file does not exist by default on all systems. If /etc/sysconfig/nfs
does not exist, create it and specify the following:
- RPCMOUNTDOPTS="-p port"
- This adds "-p port" to the rpc.mount command line:
rpc.mount -p port
.
nlockmgr
service, set the port number for the nlm_tcpport
and nlm_udpport
options in the /etc/modprobe.d/lockd.conf
file.
/var/log/messages
. Commonly, NFS fails to start if you specify a port number that is already in use. After editing /etc/sysconfig/nfs
, you need to restart the nfs-config
service for the new values to take effect in Red Hat Enterprise Linux 7.2 and prior by running:
Then, restart the NFS server:#
systemctl restart nfs-config
Run#
systemctl restart nfs-server
rpcinfo -p
to confirm the changes have taken effect.
Note
/proc/sys/fs/nfs/nfs_callback_tcpport
and allow the server to connect to that port on the client.
mountd
, statd
, and lockd
are not required in a pure NFSv4 environment.
8.6.3.1. Discovering NFS exports
- On any server that supports NFSv3, use the
showmount
command:$
showmount -e myserver
Export list for mysever /exports/foo /exports/bar - On any server that supports NFSv4,
mount
the root directory and look around.#
mount myserver:/ /mnt/
#
cd /mnt/
exports#
ls exports
foo bar
Note
8.6.4. Accessing RPC Quota through a Firewall
Procedure 8.1. Making RPC Quota Accessible Behind a Firewall
- To enable the
rpc-rquotad
service, use the following command:#
systemctl enable rpc-rquotad
- To start the
rpc-rquotad
service, use the following command:#
systemctl start rpc-rquotad
rpc-rquotad
is, if enabled, started automatically after starting thenfs-server
service. - To make the quota RPC service accessible behind a firewall, UDP or TCP port
875
need to be open. The default port number is defined in the/etc/services
file.You can override the default port number by appending-p port-number
to theRPCRQUOTADOPTS
variable in the/etc/sysconfig/rpc-rquotad
file. - Restart
rpc-rquotad
for changes in the/etc/sysconfig/rpc-rquotad
file to take effect:#
systemctl restart rpc-rquotad
Setting Quotas from Remote Hosts
-S
option to the RPCRQUOTADOPTS
variable in the /etc/sysconfig/rpc-rquotad
file.
rpc-rquotad
for changes in the /etc/sysconfig/rpc-rquotad
file to take effect:
#
systemctl restart rpc-rquotad
8.6.5. Hostname Formats
- Single machine
- A fully-qualified domain name (that can be resolved by the server), hostname (that can be resolved by the server), or an IP address.
- Series of machines specified with wildcards
- Use the
*
or?
character to specify a string match. Wildcards are not to be used with IP addresses; however, they may accidentally work if reverse DNS lookups fail. When specifying wildcards in fully qualified domain names, dots (.
) are not included in the wildcard. For example,*.example.com
includesone.example.com
but does notinclude one.two.example.com
. - IP networks
- Use a.b.c.d/z, where a.b.c.d is the network and z is the number of bits in the netmask (for example 192.168.0.0/24). Another acceptable format is a.b.c.d/netmask, where a.b.c.d is the network and netmask is the netmask (for example, 192.168.100.8/255.255.255.0).
- Netgroups
- Use the format @group-name, where group-name is the NIS netgroup name.
8.6.6. Enabling NFS over RDMA (NFSoRDMA)
- Install the rdma and rdma-core packages.The
/etc/rdma/rdma.conf
file contains a line that setsXPRTRDMA_LOAD=yes
by default, which requests therdma
service to load the NFSoRDMA client module. - To enable automatic loading of NFSoRDMA server modules, add
SVCRDMA_LOAD=yes
on a new line in/etc/rdma/rdma.conf
.RPCNFSDARGS="--rdma=20049"
in the/etc/sysconfig/nfs
file specifies the port number on which the NFSoRDMA service listens for clients. RFC 5667 specifies that servers must listen on port20049
when providing NFSv4 services over RDMA. - Restart the
nfs
service after editing the/etc/rdma/rdma.conf
file:#
systemctl restart nfs
Note that with earlier kernel versions, a system reboot is needed after editing/etc/rdma/rdma.conf
for the changes to take effect.
8.6.7. Configuring an NFSv4-only Server
rpcbind
service to listen on the network.
Requested NFS version or transport protocol is not supported.
Procedure 8.2. Configuring an NFSv4-only Server
- Disable NFSv2, NFSv3, and UDP by adding the following line to the
/etc/sysconfig/nfs
configuration file:RPCNFSDARGS="-N 2 -N 3 -U"
- Optionally, disable listening for the
RPCBIND
,MOUNT
, andNSM
protocol calls, which are not necessary in the NFSv4-only case.The effects of disabling these options are:- Clients that attempt to mount shares from your server using NFSv2 or NFSv3 become unresponsive.
- The NFS server itself is unable to mount NFSv2 and NFSv3 file systems.
To disable these options:- Add the following to the
/etc/sysconfig/nfs
file:RPCMOUNTDOPTS="-N 2 -N 3"
- Disable related services:
#
systemctl mask --now rpc-statd.service rpcbind.service rpcbind.socket
- Restart the NFS server:
#
systemctl restart nfs
The changes take effect as soon as you start or restart the NFS server.
Verifying the NFSv4-only Configuration
netstat
utility.
- The following is an example
netstat
output on an NFSv4-only server; listening forRPCBIND
,MOUNT
, andNSM
is also disabled. Here,nfs
is the only listening NFS service:#
netstat -ltu
Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:nfs 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN tcp 0 0 localhost:smtp 0.0.0.0:* LISTEN tcp6 0 0 [::]:nfs [::]:* LISTEN tcp6 0 0 [::]:12432 [::]:* LISTEN tcp6 0 0 [::]:12434 [::]:* LISTEN tcp6 0 0 localhost:7092 [::]:* LISTEN tcp6 0 0 [::]:ssh [::]:* LISTEN udp 0 0 localhost:323 0.0.0.0:* udp 0 0 0.0.0.0:bootpc 0.0.0.0:* udp6 0 0 localhost:323 [::]:* - In comparison, the
netstat
output before configuring an NFSv4-only server includes thesunrpc
andmountd
services:#
netstat -ltu
Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:nfs 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:36069 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:52364 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:sunrpc 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:mountd 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN tcp 0 0 localhost:smtp 0.0.0.0:* LISTEN tcp6 0 0 [::]:34941 [::]:* LISTEN tcp6 0 0 [::]:nfs [::]:* LISTEN tcp6 0 0 [::]:sunrpc [::]:* LISTEN tcp6 0 0 [::]:mountd [::]:* LISTEN tcp6 0 0 [::]:12432 [::]:* LISTEN tcp6 0 0 [::]:56881 [::]:* LISTEN tcp6 0 0 [::]:12434 [::]:* LISTEN tcp6 0 0 localhost:7092 [::]:* LISTEN tcp6 0 0 [::]:ssh [::]:* LISTEN udp 0 0 localhost:323 0.0.0.0:* udp 0 0 0.0.0.0:37190 0.0.0.0:* udp 0 0 0.0.0.0:876 0.0.0.0:* udp 0 0 localhost:877 0.0.0.0:* udp 0 0 0.0.0.0:mountd 0.0.0.0:* udp 0 0 0.0.0.0:38588 0.0.0.0:* udp 0 0 0.0.0.0:nfs 0.0.0.0:* udp 0 0 0.0.0.0:bootpc 0.0.0.0:* udp 0 0 0.0.0.0:sunrpc 0.0.0.0:* udp6 0 0 localhost:323 [::]:* udp6 0 0 [::]:57683 [::]:* udp6 0 0 [::]:876 [::]:* udp6 0 0 [::]:mountd [::]:* udp6 0 0 [::]:40874 [::]:* udp6 0 0 [::]:nfs [::]:* udp6 0 0 [::]:sunrpc [::]:*
8.7. Securing NFS
8.7.1. NFS Security with AUTH_SYS and Export Controls
AUTH_SYS
(also called AUTH_UNIX
) which relies on the client to state the UID and GID's of the user. Be aware that this means a malicious or misconfigured client can easily get this wrong and allow a user access to files that it should not.
rpcbind
[1] service with TCP wrappers. Creating rules with iptables
can also limit access to ports used by rpcbind
, rpc.mountd
, and rpc.nfsd
.
rpcbind
, refer to man iptables
.
8.7.2. NFS Security with AUTH_GSS
Configuring Kerberos
Procedure 8.3. Configuring an NFS Server and Client for IdM to Use RPCSEC_GSS
- Create the
nfs/hostname.domain@REALM
principal on the NFS server side. - Create the
host/hostname.domain@REALM
principal on both the server and the client side.Note
The hostname must be identical to the NFS server hostname. - Add the corresponding keys to keytabs for the client and server.
For instructions, see the Adding and Editing Service Entries and Keytabs and Setting up a Kerberos-aware NFS Server sections in the Red Hat Enterprise Linux 7 Linux Domain Identity, Authentication, and Policy Guide.- On the server side, use the
sec=
option to enable the wanted security flavors. To enable all security flavors as well as non-cryptographic mounts:/export *(sec=sys:krb5:krb5i:krb5p)
Valid security flavors to use with thesec=
option are:sys
: no cryptographic protection, the defaultkrb5
: authentication onlykrb5i
: integrity protectionkrb5p
: privacy protection
- On the client side, add
sec=krb5
(orsec=krb5i
, orsec=krb5p
, depending on the setup) to the mount options:# mount -o sec=krb5 server:/export /mnt
For information on how to configure a NFS client, see the Setting up a Kerberos-aware NFS Client section in the Red Hat Enterprise Linux 7 Linux Domain Identity, Authentication, and Policy Guide.
Additional Resources
- Although Red Hat recommends using IdM, Active Directory (AD) Kerberos servers are also supported. For details, see the following Red Hat Knowledgebase article: How to set up NFS using Kerberos authentication on RHEL 7 using SSSD and Active Directory.
- If you need to write files as root on the Kerberos-secured NFS share and keep root ownership on these files, see https://access.redhat.com/articles/4040141. Note that this configuration is not recommended.
- For more information on NFS client configuration, see the exports(5) and nfs(5) manual pages, and Section 8.4, “Common NFS Mount Options”.
- For further information on the
RPCSEC_GSS
framework, including howgssproxy
andrpc.gssd
inter-operate, see the GSSD flow description.
8.7.2.1. NFS Security with NFSv4
MOUNT
protocol for mounting file systems. The MOUNT
protocol presented a security risk because of the way the protocol processed file handles.
8.7.3. File Permissions
su -
command to access any files with the NFS share.
nobody
. Root squashing is controlled by the default option root_squash
; for more information about this option, refer to Section 8.6.1, “The /etc/exports
Configuration File”. If possible, never disable root squashing.
all_squash
option. This option makes every user accessing the exported file system take the user ID of the nfsnobody
user.
8.8. NFS and rpcbind
Note
rpcbind
service for backward compatibility.
rpcbind
, see Section 8.6.7, “Configuring an NFSv4-only Server”.
rpcbind
[1] utility maps RPC services to the ports on which they listen. RPC processes notify rpcbind
when they start, registering the ports they are listening on and the RPC program numbers they expect to serve. The client system then contacts rpcbind
on the server with a particular RPC program number. The rpcbind
service redirects the client to the proper port number so it can communicate with the requested service.
rpcbind
to make all connections with incoming client requests, rpcbind
must be available before any of these services start.
rpcbind
service uses TCP wrappers for access control, and access control rules for rpcbind
affect all RPC-based services. Alternatively, it is possible to specify access control rules for each of the NFS RPC daemons. The man
pages for rpc.mountd
and rpc.statd
contain information regarding the precise syntax for these rules.
8.8.1. Troubleshooting NFS and rpcbind
rpcbind
[1] provides coordination between RPC services and the port numbers used to communicate with them, it is useful to view the status of current RPC services using rpcbind
when troubleshooting. The rpcinfo
command shows each RPC-based service with port numbers, an RPC program number, a version number, and an IP protocol type (TCP or UDP).
rpcbind
, use the following command:
# rpcinfo -p
Example 8.7. rpcinfo -p
command output
program vers proto port service 100021 1 udp 32774 nlockmgr 100021 3 udp 32774 nlockmgr 100021 4 udp 32774 nlockmgr 100021 1 tcp 34437 nlockmgr 100021 3 tcp 34437 nlockmgr 100021 4 tcp 34437 nlockmgr 100011 1 udp 819 rquotad 100011 2 udp 819 rquotad 100011 1 tcp 822 rquotad 100011 2 tcp 822 rquotad 100003 2 udp 2049 nfs 100003 3 udp 2049 nfs 100003 2 tcp 2049 nfs 100003 3 tcp 2049 nfs 100005 1 udp 836 mountd 100005 1 tcp 839 mountd 100005 2 udp 836 mountd 100005 2 tcp 839 mountd 100005 3 udp 836 mountd 100005 3 tcp 839 mountd
rpcbind
will be unable to map RPC requests from clients for that service to the correct port. In many cases, if NFS is not present in rpcinfo
output, restarting NFS causes the service to correctly register with rpcbind
and begin working.
rpcinfo
, see its man
page.
8.9. pNFS
Note
pNFS Flex Files
Mounting pNFS Shares
- To enable pNFS functionality, mount shares from a pNFS-enabled server with NFS version 4.1 or later:
#
mount -t nfs -o v4.1 server:/remote-export /local-directory
After the server is pNFS-enabled, thenfs_layout_nfsv41_files
kernel is automatically loaded on the first mount. The mount entry in the output should containminorversion=1
. Use the following command to verify the module was loaded:$
lsmod | grep nfs_layout_nfsv41_files
- To mount an NFS share with the Flex Files feature from a server that supports Flex Files, use NFS version 4.2 or later:
#
mount -t nfs -o v4.2 server:/remote-export /local-directory
Verify that thenfs_layout_flexfiles
module has been loaded:$
lsmod | grep nfs_layout_flexfiles
Additional Resources
8.10. Enabling pNFS SCSI Layouts in NFS
Prerequisites
- Both the client and the server must be able to send SCSI commands to the same block device. That is, the block device must be on a shared SCSI bus.
- The block device must contain an XFS file system.
- The SCSI device must support SCSI Persistent Reservations as described in the SCSI-3 Primary Commands specification.
8.10.1. pNFS SCSI Layouts
Operations Between the Client and the Server
LAYOUTGET
operation. The server responds with the location of the file on the SCSI device. The client might need to perform an additional operation of GETDEVICEINFO
to determine which SCSI device to use. If these operations work correctly, the client can issue I/O requests directly to the SCSI device instead of sending READ
and WRITE
operations to the server.
READ
and WRITE
operations to the server instead of sending I/O requests directly to the SCSI device.
Device Reservations
8.10.2. Checking for a SCSI Device Compatible with pNFS
Prerequisites
- Install the sg3_utils package:
# yum install sg3_utils
Procedure 8.4. Checking for a SCSI Device Compatible with pNFS
- On both the server and client, check for the proper SCSI device support:
# sg_persist --in --report-capabilities --verbose path-to-scsi-device
Ensure that the Persist Through Power Loss Active (PTPL_A
) bit is set.Example 8.8. A SCSI device that supports pNFS SCSI
The following is an example ofsg_persist
output for a SCSI device that supports pNFS SCSI. ThePTPL_A
bit reports1
.inquiry cdb: 12 00 00 00 24 00 Persistent Reservation In cmd: 5e 02 00 00 00 00 00 20 00 00 LIO-ORG block11 4.0 Peripheral device type: disk Report capabilities response: Compatible Reservation Handling(CRH): 1 Specify Initiator Ports Capable(SIP_C): 1 All Target Ports Capable(ATP_C): 1 Persist Through Power Loss Capable(PTPL_C): 1 Type Mask Valid(TMV): 1 Allow Commands: 1 Persist Through Power Loss Active(PTPL_A): 1 Support indicated in Type mask: Write Exclusive, all registrants: 1 Exclusive Access, registrants only: 1 Write Exclusive, registrants only: 1 Exclusive Access: 1 Write Exclusive: 1 Exclusive Access, all registrants: 1
Additional Resources
- The sg_persist(8) man page
8.10.3. Setting up pNFS SCSI on the Server
Procedure 8.5. Setting up pNFS SCSI on the Server
- On the server, mount the XFS file system created on the SCSI device.
- Configure the NFS server to export NFS version 4.1 or higher. Set the following option in the
[nfsd]
section of the/etc/nfs.conf
file:[nfsd] vers4.1=y
- Configure the NFS server to export the XFS file system over NFS with the
pnfs
option:Example 8.9. An Entry in /etc/exports to Export pNFS SCSI
The following entry in the/etc/exports
configuration file exports the file system mounted at/exported/directory/
to theallowed.example.com
client as a pNFS SCSI layout:/exported/directory allowed.example.com(pnfs)
Additional Resources
- For more information on configuring an NFS server, see Section 8.6, “Configuring the NFS Server”.
8.10.4. Setting up pNFS SCSI on the Client
Prerequisites
- The NFS server is configured to export an XFS file system over pNFS SCSI. See Section 8.10.3, “Setting up pNFS SCSI on the Server”.
Procedure 8.6. Setting up pNFS SCSI on the Client
- On the client, mount the exported XFS file system using NFS version 4.1 or higher:
# mount -t nfs -o nfsvers=4.1 host:/remote/export /local/directory
Do not mount the XFS file system directly without NFS.
Additional Resources
- For more information on mounting NFS shares, see Section 8.2, “Configuring NFS Client”.
8.10.5. Releasing the pNFS SCSI Reservation on the Server
Prerequisites
- Install the sg3_utils package:
# yum install sg3_utils
Procedure 8.7. Releasing the pNFS SCSI Reservation on the Server
- Query an existing reservation on the server:
# sg_persist --read-reservation path-to-scsi-device
Example 8.10. Querying a Reservation on /dev/sda
# sg_persist --read-reservation /dev/sda LIO-ORG block_1 4.0 Peripheral device type: disk PR generation=0x8, Reservation follows: Key=0x100000000000000 scope: LU_SCOPE, type: Exclusive Access, registrants only
- Remove the existing registration on the server:
# sg_persist --out \ --release \ --param-rk=reservation-key \ --prout-type=6 \ path-to-scsi-device
Example 8.11. Removing a Reservation on /dev/sda
# sg_persist --out \ --release \ --param-rk=0x100000000000000 \ --prout-type=6 \ /dev/sda LIO-ORG block_1 4.0 Peripheral device type: disk
Additional Resources
- The sg_persist(8) man page
8.10.6. Monitoring pNFS SCSI Layouts Functionality
Prerequisites
- A pNFS SCSI client and server are configured.
8.10.6.1. Checking pNFS SCSI Operations from the Server Using nfsstat
nfsstat
utility to monitor pNFS SCSI operations from the server.
Procedure 8.8. Checking pNFS SCSI Operations from the Server Using nfsstat
- Monitor the operations serviced from the server:
# watch --differences \ "nfsstat --server | egrep --after-context=1 read\|write\|layout" Every 2.0s: nfsstat --server | egrep --after-context=1 read\|write\|layout putrootfh read readdir readlink remove rename 2 0% 0 0% 1 0% 0 0% 0 0% 0 0% -- setcltidconf verify write rellockowner bc_ctl bind_conn 0 0% 0 0% 0 0% 0 0% 0 0% 0 0% -- getdevlist layoutcommit layoutget layoutreturn secinfononam sequence 0 0% 29 1% 49 1% 5 0% 0 0% 2435 86%
- The client and server use pNFS SCSI operations when:
- The
layoutget
,layoutreturn
, andlayoutcommit
counters increment. This means that the server is serving layouts. - The server
read
andwrite
counters do not increment. This means that the clients are performing I/O requests directly to the SCSI devices.
8.10.6.2. Checking pNFS SCSI Operations from the Client Using mountstats
/proc/self/mountstats
file to monitor pNFS SCSI operations from the client.
Procedure 8.9. Checking pNFS SCSI Operations from the Client Using mountstats
- List the per-mount operation counters:
# cat /proc/self/mountstats \ | awk /scsi_lun_0/,/^$/ \ | egrep device\|READ\|WRITE\|LAYOUT device 192.168.122.73:/exports/scsi_lun_0 mounted on /mnt/rhel7/scsi_lun_0 with fstype nfs4 statvers=1.1 nfsv4: bm0=0xfdffbfff,bm1=0x40f9be3e,bm2=0x803,acl=0x3,sessions,pnfs=LAYOUT_SCSI READ: 0 0 0 0 0 0 0 0 WRITE: 0 0 0 0 0 0 0 0 READLINK: 0 0 0 0 0 0 0 0 READDIR: 0 0 0 0 0 0 0 0 LAYOUTGET: 49 49 0 11172 9604 2 19448 19454 LAYOUTCOMMIT: 28 28 0 7776 4808 0 24719 24722 LAYOUTRETURN: 0 0 0 0 0 0 0 0 LAYOUTSTATS: 0 0 0 0 0 0 0 0
- In the results:
- The
LAYOUT
statistics indicate requests where the client and server use pNFS SCSI operations. - The
READ
andWRITE
statistics indicate requests where the client and server fall back to NFS operations.
8.11. NFS References
Installed Documentation
man mount
— Contains a comprehensive look at mount options for both NFS server and client configurations.man fstab
— Provides detail for the format of the/etc/fstab
file used to mount file systems at boot-time.man nfs
— Provides details on NFS-specific file system export and mount options.man exports
— Shows common options used in the/etc/exports
file when exporting NFS file systems.
Useful Websites
- http://linux-nfs.org — The current site for developers where project status updates can be viewed.
- http://nfs.sourceforge.net/ — The old home for developers which still contains a lot of useful information.
- http://www.citi.umich.edu/projects/nfsv4/linux/ — An NFSv4 for Linux 2.6 kernel resource.
- http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.111.4086 — An excellent whitepaper on the features and enhancements of the NFS Version 4 protocol.
rpcbind
service replaces portmap
, which was used in previous versions of Red Hat Enterprise Linux to map RPC program numbers to IP address port number combinations. For more information, refer to Section 8.1.1, “Required Services”.
Chapter 9. Server Message Block (SMB)
cifs-utils
utility to mount SMB shares from a remote server.
Note
cifs
.
Chapter 10. FS-Cache
Figure 10.1. FS-Cache Overview
cachefs
on Solaris, FS-Cache allows a file system on a server to interact directly with a client's local cache without creating an overmounted file system. With NFS, a mount option instructs the client to mount the NFS share with FS-cache enabled.
cachefiles
). In this case, FS-Cache requires a mounted block-based file system that supports bmap
and extended attributes (e.g. ext3) as its cache back end.
Note
10.1. Performance Guarantee
10.2. Setting up a Cache
cachefiles
caching back end. The cachefilesd
daemon initiates and manages cachefiles
. The /etc/cachefilesd.conf
file controls how cachefiles
provides caching services.
$ dir /path/to/cache
/etc/cachefilesd.conf
as /var/cache/fscache
, as in:
$ dir /var/cache/fscache
/var/cache/fscache
:
#
semanage fcontext -a -e /var/cache/fscache /path/to/cache
#
restorecon -Rv /path/to/cache
Note
#
semanage permissive -a cachefilesd_t
#
semanage permissive -a cachefiles_kernel_t
/path/to/cache
. On a laptop, it is advisable to use the root file system (/
) as the host file system, but for a desktop machine it would be more prudent to mount a disk partition specifically for the cache.
- ext3 (with extended attributes enabled)
- ext4
- Btrfs
- XFS
device
), use:
# tune2fs -o user_xattr /dev/device
# mount /dev/device /path/to/cache -o user_xattr
cachefilesd
service:
#
systemctl start cachefilesd
cachefilesd
to start at boot time, execute the following command as root:
#
systemctl enable cachefilesd
10.3. Using the Cache with NFS
-o fsc
option to the mount
command:
# mount nfs-share:/ /mount/point -o fsc
/mount/point
will go through the cache, unless the file is opened for direct I/O or writing. For more information, see Section 10.3.2, “Cache Limitations with NFS”. NFS indexes cache contents using NFS file handle, not the file name, which means hard-linked files share the cache correctly.
10.3.1. Cache Sharing
- Level 1: Server details
- Level 2: Some mount options; security type; FSID; uniquifier
- Level 3: File Handle
- Level 4: Page number in file
Example 10.1. Cache Sharing
mount
commands:
mount home0:/disk0/fred /home/fred -o fsc
mount home0:/disk0/jim /home/jim -o fsc
/home/fred
and /home/jim
likely share the superblock as they have the same options, especially if they come from the same volume/partition on the NFS server (home0
). Now, consider the next two subsequent mount commands:
mount home0:/disk0/fred /home/fred -o fsc,rsize=230
mount home0:/disk0/jim /home/jim -o fsc,rsize=231
/home/fred
and /home/jim
will not share the superblock as they have different network access parameters, which are part of the Level 2 key. The same goes for the following mount sequence:
mount home0:/disk0/fred /home/fred1 -o fsc,rsize=230
mount home0:/disk0/fred /home/fred2 -o fsc,rsize=231
/home/fred1
and /home/fred2
) will be cached twice.
nosharecache
parameter. Using the same example:
mount home0:/disk0/fred /home/fred -o nosharecache,fsc
mount home0:/disk0/jim /home/jim -o nosharecache,fsc
home0:/disk0/fred
and home0:/disk0/jim
. To address this, add a unique identifier on at least one of the mounts, i.e. fsc=unique-identifier
. For example:
mount home0:/disk0/fred /home/fred -o nosharecache,fsc
mount home0:/disk0/jim /home/jim -o nosharecache,fsc=jim
jim
is added to the Level 2 key used in the cache for /home/jim
.
10.3.2. Cache Limitations with NFS
- Opening a file from a shared file system for direct I/O automatically bypasses the cache. This is because this type of access must be direct to the server.
- Opening a file from a shared file system for writing will not work on NFS version 2 and 3. The protocols of these versions do not provide sufficient coherency management information for the client to detect a concurrent write to the same file from another client.
- Opening a file from a shared file system for either direct I/O or writing flushes the cached copy of the file. FS-Cache will not cache the file again until it is no longer opened for direct I/O or writing.
- Furthermore, this release of FS-Cache only caches regular NFS files. FS-Cache will not cache directories, symlinks, device files, FIFOs and sockets.
10.4. Setting Cache Cull Limits
cachefilesd
daemon works by caching remote data from shared file systems to free space on the disk. This could potentially consume all available free space, which could be bad if the disk also housed the root partition. To control this, cachefilesd
tries to maintain a certain amount of free space by discarding old objects (i.e. accessed less recently) from the cache. This behavior is known as cache culling.
/etc/cachefilesd.conf
:
- brun N% (percentage of blocks) , frun N% (percentage of files)
- If the amount of free space and the number of available files in the cache rises above both these limits, then culling is turned off.
- bcull N% (percentage of blocks), fcull N% (percentage of files)
- If the amount of available space or the number of files in the cache falls below either of these limits, then culling is started.
- bstop N% (percentage of blocks), fstop N% (percentage of files)
- If the amount of available space or the number of available files in the cache falls below either of these limits, then no further allocation of disk space or files is permitted until culling has raised things above these limits again.
N
for each setting is as follows:
brun
/frun
- 10%bcull
/fcull
- 7%bstop
/fstop
- 3%
- 0 ≤
bstop
<bcull
<brun
< 100 - 0 ≤
fstop
<fcull
<frun
< 100
df
program.
Important
10.5. Statistical Information
# cat /proc/fs/fscache/stats
/usr/share/doc/kernel-doc-version/Documentation/filesystems/caching/fscache.txt
10.6. FS-Cache References
cachefilesd
and how to configure it, see man cachefilesd
and man cachefilesd.conf
. The following kernel documents also provide additional information:
/usr/share/doc/cachefilesd-version-number/README
/usr/share/man/man5/cachefilesd.conf.5.gz
/usr/share/man/man8/cachefilesd.8.gz
/usr/share/doc/kernel-doc-version/Documentation/filesystems/caching/fscache.txt
Part II. Storage Administration
Chapter 11. Storage Considerations During Installation
11.1. Special Considerations
Separate Partitions for /home, /opt, /usr/local
/home
, /opt
, and /usr/local
on a separate device. This allows you to reformat the devices or file systems containing the operating system while preserving your user and application data.
DASD and zFCP Devices on IBM System Z
DASD=
parameter at the boot command line or in a CMS configuration file.
FCP_x=
lines on the boot command line (or in a CMS configuration file) allow you to specify this information for the installer.
Encrypting Block Devices Using LUKS
dm-crypt
destroys any existing formatting on that device. As such, you should decide which devices to encrypt (if any) before the new system's storage configuration is activated as part of the installation process.
Stale BIOS RAID Metadata
Warning
Note
dmraid
, which is now deprecated, use the dmraid
utility to delete it:
#
dmraid -r -E /device/
man dmraid
and Chapter 18, Redundant Array of Independent Disks (RAID).
iSCSI Detection and Configuration
FCoE Detection and Configuration
DASD
Block Devices with DIF/DIX Enabled
mmap(2)
-based I/O will not work reliably, as there are no interlocks in the buffered write path to prevent buffered data from being overwritten after the DIF/DIX checksum has been calculated.
mmap(2)
I/O, so it is not possible to work around these errors caused by overwrites.
O_DIRECT
. Such applications should use the raw block device. Alternatively, it is also safe to use the XFS file system on a DIF/DIX enabled block device, as long as only O_DIRECT
I/O is issued through the file system. XFS is the only file system that does not fall back to buffered I/O when doing certain allocation operations.
O_DIRECT
I/O and DIF/DIX hardware should use DIF/DIX.
Chapter 12. File System Check
fsck
tools, where fsck
is a shortened version of file system check.
Note
/etc/fstab
at boot-time. For journaling file systems, this is usually a very short operation, because the file system's metadata journaling ensures consistency even after a crash.
Important
/etc/fstab
to 0
.
12.1. Best Practices for fsck
- Dry run
- Most file system checkers have a mode of operation which checks but does not repair the file system. In this mode, the checker prints any errors that it finds and actions that it would have taken, without actually modifying the file system.
Note
Later phases of consistency checking may print extra errors as it discovers inconsistencies which would have been fixed in early phases if it were running in repair mode. - Operate first on a file system image
- Most file systems support the creation of a metadata image, a sparse copy of the file system which contains only metadata. Because file system checkers operate only on metadata, such an image can be used to perform a dry run of an actual file system repair, to evaluate what changes would actually be made. If the changes are acceptable, the repair can then be performed on the file system itself.
Note
Severely damaged file systems may cause problems with metadata image creation. - Save a file system image for support investigations
- A pre-repair file system metadata image can often be useful for support investigations if there is a possibility that the corruption was due to a software bug. Patterns of corruption present in the pre-repair image may aid in root-cause analysis.
- Operate only on unmounted file systems
- A file system repair must be run only on unmounted file systems. The tool must have sole access to the file system or further damage may result. Most file system tools enforce this requirement in repair mode, although some only support check-only mode on a mounted file system. If check-only mode is run on a mounted file system, it may find spurious errors that would not be found when run on an unmounted file system.
- Disk errors
- File system check tools cannot repair hardware problems. A file system must be fully readable and writable if repair is to operate successfully. If a file system was corrupted due to a hardware error, the file system must first be moved to a good disk, for example with the
dd(8)
utility.
12.2. File System-Specific Information for fsck
12.2.1. ext2, ext3, and ext4
e2fsck
binary to perform file system checks and repairs. The file names fsck.ext2
, fsck.ext3
, and fsck.ext4
are hardlinks to this same binary. These binaries are run automatically at boot time and their behavior differs based on the file system being checked and the state of the file system.
e2fsck
finds that a file system is marked with such an error, e2fsck
performs a full check after replaying the journal (if present).
e2fsck
may ask for user input during the run if the -p
option is not specified. The -p
option tells e2fsck
to automatically do all repairs that may be done safely. If user intervention is required, e2fsck
indicates the unfixed problem in its output and reflect this status in the exit code.
e2fsck
run-time options include:
-n
- No-modify mode. Check-only operation.
-b
superblock- Specify block number of an alternate suprerblock if the primary one is damaged.
-f
- Force full check even if the superblock has no recorded errors.
-j
journal-dev- Specify the external journal device, if any.
-p
- Automatically repair or "preen" the file system with no user input.
-y
- Assume an answer of "yes" to all questions.
e2fsck
are specified in the e2fsck(8)
manual page.
e2fsck
while running:
- Inode, block, and size checks.
- Directory structure checks.
- Directory connectivity checks.
- Reference count checks.
- Group summary info checks.
e2image(8)
utility can be used to create a metadata image prior to repair for diagnostic or testing purposes. The -r
option should be used for testing purposes in order to create a sparse file of the same size as the file system itself. e2fsck
can then operate directly on the resulting file. The -Q
option should be specified if the image is to be archived or provided for diagnostic. This creates a more compact file format suitable for transfer.
12.2.2. XFS
xfs_repair
tool.
Note
fsck.xfs
binary is present in the xfsprogs package, this is present only to satisfy initscripts that look for an fsck.file system
binary at boot time. fsck.xfs
immediately exits with an exit code of 0.
xfs_check
tool. This tool is very slow and does not scale well for large file systems. As such, it has been deprecated in favor of xfs_repair -n
.
xfs_repair
to operate. If the file system was not cleanly unmounted, it should be mounted and unmounted prior to using xfs_repair
. If the log is corrupt and cannot be replayed, the -L
option may be used to zero the log.
Important
-L
option must only be used if the log cannot be replayed. The option discards all metadata updates in the log and results in further inconsistencies.
xfs_repair
in a dry run, check-only mode by using the -n
option. No changes will be made to the file system when this option is specified.
xfs_repair
takes very few options. Commonly used options include:
-n
- No modify mode. Check-only operation.
-L
- Zero metadata log. Use only if log cannot be replayed with mount.
-m
maxmem- Limit memory used during run to maxmem MB. 0 can be specified to obtain a rough estimate of the minimum memory required.
-l
logdev- Specify the external log device, if present.
xfs_repair
are specified in the xfs_repair(8)
manual page.
xfs_repair
while running:
- Inode and inode blockmap (addressing) checks.
- Inode allocation map checks.
- Inode size checks.
- Directory checks.
- Pathname checks.
- Link count checks.
- Freemap checks.
- Super block checks.
xfs_repair(8)
manual page.
xfs_repair
is not interactive. All operations are performed automatically with no input from the user.
xfs_metadump(8)
and xfs_mdrestore(8)
utilities may be used.
12.2.3. Btrfs
Note
btrfsck
tool is used to check and repair btrfs file systems. This tool is still in early development and may not detect or repair all types of file system corruption.
btrfsck
does not make changes to the file system; that is, it runs check-only mode by default. If repairs are desired the --repair
option must be specified.
btrfsck
while running:
- Extent checks.
- File system root checks.
- Root reference count checks.
btrfs-image(8)
utility can be used to create a metadata image prior to repair for diagnostic or testing purposes.
Chapter 13. Partitions
Note
- View the existing partition table.
- Change the size of existing partitions.
- Add partitions from free space or additional hard drives.
#
parted /dev/sda
Manipulating Partitions on Devices in Use
Modifying the Partition Table
#
partx --update --nr partition-number disk
- Boot the system in rescue mode if the partitions on the disk are impossible to unmount, for example in the case of a system disk.
- When prompted to mount the file system, select.
umount
command and turn off all the swap space on the hard drive with the swapoff
command.
parted
Commands”.
Important
Command | Description |
---|---|
help | Display list of available commands |
mklabel label | Create a disk label for the partition table |
mkpart part-type [fs-type] start-mb end-mb | Make a partition without creating a new file system |
name minor-num name | Name the partition for Mac and PC98 disklabels only |
print | Display the partition table |
quit | Quit parted |
rescue start-mb end-mb | Rescue a lost partition from start-mb to end-mb |
rm minor-num | Remove the partition |
select device | Select a different device to configure |
set minor-num flag state | Set the flag on a partition; state is either on or off |
toggle [NUMBER [FLAG] | Toggle the state of FLAG on partition NUMBER |
unit UNIT | Set the default unit to UNIT |
13.1. Viewing the Partition Table
- Start parted.
- Use the following command to view the partition table:
(parted)
print
Example 13.1. Partition Table
Model: ATA ST3160812AS (scsi) Disk /dev/sda: 160GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 32.3kB 107MB 107MB primary ext3 boot 2 107MB 105GB 105GB primary ext3 3 105GB 107GB 2147MB primary linux-swap 4 107GB 160GB 52.9GB extended root 5 107GB 133GB 26.2GB logical ext3 6 133GB 133GB 107MB logical ext3 7 133GB 160GB 26.6GB logical lvm
- Model: ATA ST3160812AS (scsi): explains the disk type, manufacturer, model number, and interface.
- Disk /dev/sda: 160GB: displays the file path to the block device and the storage capacity.
- Partition Table: msdos: displays the disk label type.
- In the partition table,
Number
is the partition number. For example, the partition with minor number 1 corresponds to/dev/sda1
. TheStart
andEnd
values are in megabytes. ValidTypes
are metadata, free, primary, extended, or logical. TheFile system
is the file system type. The Flags column lists the flags set for the partition. Available flags are boot, root, swap, hidden, raid, lvm, or lba.
File system
in the partition table can be any of the following:
- ext2
- ext3
- fat16
- fat32
- hfs
- jfs
- linux-swap
- ntfs
- reiserfs
- hp-ufs
- sun-ufs
- xfs
File system
of a device shows no value, this means that its file system type is unknown.
13.2. Creating a Partition
Warning
Procedure 13.1. Creating a Partition
- Before creating a partition, boot into rescue mode, or unmount any partitions on the device and turn off any swap space on the device.
- Start
parted
:# parted /dev/sda
Replace /dev/sda with the device name on which you want to create the partition. - View the current partition table to determine if there is enough free space:
(parted)
print
If there is not enough free space, you can resize an existing partition. For more information, see Section 13.5, “Resizing a Partition with fdisk”.From the partition table, determine the start and end points of the new partition and what partition type it should be. You can only have four primary partitions, with no extended partition, on a device. If you need more than four partitions, you can have three primary partitions, one extended partition, and multiple logical partitions within the extended. For an overview of disk partitions, see the appendix An Introduction to Disk Partitions in the Red Hat Enterprise Linux 7 Installation Guide. - To create partition:
(parted)
mkpart part-type name fs-type start end
Replace part-type with with primary, logical, or extended as per your requirement.Replace name with partition-name; name is required for GPT partition tables.Replace fs-type with any one of btrfs, ext2, ext3, ext4, fat16, fat32, hfs, hfs+, linux-swap, ntfs, reiserfs, or xfs; fs-type is optional.Replace start end with the size in megabytes as per your requirement.For example, to create a primary partition with an ext3 file system from 1024 megabytes until 2048 megabytes on a hard drive, type the following command:(parted)
mkpart primary 1024 2048
Note
If you use themkpartfs
command instead, the file system is created after the partition is created. However,parted
does not support creating an ext3 file system. Thus, if you wish to create an ext3 file system, usemkpart
and create the file system with themkfs
command as described later.The changes start taking place as soon as you press Enter, so review the command before executing to it. - View the partition table to confirm that the created partition is in the partition table with the correct partition type, file system type, and size using the following command:
(parted)
print
Also remember the minor number of the new partition so that you can label any file systems on it. - Exit the parted shell:
(parted)
quit
- Use the following command after parted is closed to make sure the kernel recognizes the new partition:
#
cat /proc/partitions
13.2.1. Formatting and Labeling the Partition
Procedure 13.2. Format and Label the Partition
- The partition does not have a file system. To create the
ext4
file system, use:#
mkfs.ext4 /dev/sda6
Warning
Formatting the partition permanently destroys any data that currently exists on the partition. - Label the file system on the partition. For example, if the file system on the new partition is
/dev/sda6
and you want to label itWork
, use:#
e2label /dev/sda6 "Work"
By default, the installation program uses the mount point of the partition as the label to make sure the label is unique. You can use any label you want. - Create a mount point (e.g.
/work
) as root.
13.2.2. Add the Partition to /etc/fstab
- As root, edit the
/etc/fstab
file to include the new partition using the partition's UUID.Use the commandblkid -o list
for a complete list of the partition's UUID, orblkid device
for individual device details.In/etc/fstab
:- The first column should contain
UUID=
followed by the file system's UUID. - The second column should contain the mount point for the new partition.
- The third column should be the file system type: for example,
ext4
orswap
. - The fourth column lists mount options for the file system. The word
defaults
here means that the partition is mounted at boot time with default options. - The fifth and sixth field specify backup and check options. Example values for a non-root partition are
0 2
.
- Regenerate mount units so that your system registers the new configuration:
#
systemctl daemon-reload
- Try mounting the file system to verify that the configuration works:
#
mount /work
Additional Information
- If you need more information about the format of
/etc/fstab
, see the fstab(5) man page.
13.3. Removing a Partition
Warning
Procedure 13.3. Remove a Partition
- Before removing a partition, do one of the following:
- Boot into rescue mode, or
- Unmount any partitions on the device and turn off any swap space on the device.
- Start the
parted
utility:#
parted device
Replace device with the device on which to remove the partition: for example,/dev/sda
. - View the current partition table to determine the minor number of the partition to remove:
(parted)
print
- Remove the partition with the command
rm
. For example, to remove the partition with minor number 3:(parted)
rm 3
The changes start taking place as soon as you press Enter, so review the command before committing to it. - After removing the partition, use the
print
command to confirm that it is removed from the partition table:(parted)
print
- Exit from the
parted
shell:(parted)
quit
- Examine the content of the
/proc/partitions
file to make sure the kernel knows the partition is removed:#
cat /proc/partitions
- Remove the partition from the
/etc/fstab
file. Find the line that declares the removed partition, and remove it from the file. - Regenerate mount units so that your system registers the new
/etc/fstab
configuration:#
systemctl daemon-reload
13.4. Setting a Partition Type
systemd-gpt-auto-generator
, which use the partition type to, for example, automatically identify and mount devices.
fdisk
utility and use the t
command to set the partition type. The following example shows how to change the partition type of the first partition to 0x83, default on Linux:
#
fdisk /dev/sdc
Command (m for help):t
Selected partition1
Partition type (type L to list all types):83
Changed type of partition 'Linux LVM' to 'Linux'.
parted
utility provides some control of partition types by trying to map the partition type to 'flags', which is not convenient for end users. The parted
utility can handle only certain partition types, for example LVM or RAID. To remove, for example, the lvm flag from the first partition with parted
, use:
#
parted /dev/sdc 'set 1 lvm off'
13.5. Resizing a Partition with fdisk
fdisk
utility allows you to create and manipulate GPT, MBR, Sun, SGI, and BSD partition tables. On disks with a GUID Partition Table (GPT), using the parted
utility is recommended, as fdisk
GPT support is in an experimental phase.
fdisk
is by deleting and recreating the partition.
Important
Procedure 13.4. Resizing a Partition
fdisk
:
- Unmount the device:
#
umount /dev/vda
- Run
fdisk disk_name
. For example:#
fdisk /dev/vda
Welcome to fdisk (util-linux 2.23.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): - Use the
p
option to determine the line number of the partition to be deleted.Command (m for help): p Disk /dev/vda: 16.1 GB, 16106127360 bytes, 31457280 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x0006d09a Device Boot Start End Blocks Id System /dev/vda1 * 2048 1026047 512000 83 Linux /dev/vda2 1026048 31457279 15215616 8e Linux LVM
- Use the
d
option to delete a partition. If there is more than one partition available,fdisk
prompts you to provide a number of the partition to delete:Command (m for help): d Partition number (1,2, default 2): 2 Partition 2 is deleted
- Use the
n
option to create a partition and follow the prompts. Allow enough space for any future resizing. Thefdisk
default behavior (pressEnter
) is to use all space on the device. You can specify the end of the partition by sectors, or specify a human-readable size by using+<size><suffix>
, for example +500M, or +10G.Red Hat recommends using the human-readable size specification if you do not want to use all free space, asfdisk
aligns the end of the partition with the physical sectors. If you specify the size by providing an exact number (in sectors),fdisk
does not align the end of the partition.Command (m for help): n Partition type: p primary (1 primary, 0 extended, 3 free) e extended Select (default p): *Enter* Using default response p Partition number (2-4, default 2): *Enter* First sector (1026048-31457279, default 1026048): *Enter* Using default value 1026048 Last sector, +sectors or +size{K,M,G} (1026048-31457279, default 31457279): +500M Partition 2 of type Linux and of size 500 MiB is set
- Set the partition type to LVM:
Command (m for help): t Partition number (1,2, default 2): *Enter* Hex code (type L to list all codes): 8e Changed type of partition 'Linux' to 'Linux LVM'
- Write the changes with the
w
option when you are sure the changes are correct, as errors can cause instability with the selected partition. - Run
e2fsck
on the device to check for consistency:#
e2fsck /dev/vda
e2fsck 1.41.12 (17-May-2010) Pass 1:Checking inodes, blocks, and sizes Pass 2:Checking directory structure Pass 3:Checking directory connectivity Pass 4:Checking reference counts Pass 5:Checking group summary information ext4-1:11/131072 files (0.0% non-contiguous),27050/524128 blocks - Mount the device:
#
mount /dev/vda
Chapter 14. Creating and Maintaining Snapshots with Snapper
14.1. Creating Initial Snapper Configuration
Warning
sudo
infrastructure instead.
Note
Procedure 14.1. Creating a Snapper Configuration File
- Create or choose either:
- A thinly-provisioned logical volume with a Red Hat supported file system on top of it, or
- A Btrfs subvolume.
- Mount the file system.
- Create the configuration file that defines this volume.For LVM2:
#
snapper -c config_name create-config -f "lvm(fs_type)" /mount-point
For example, to create a configuration file called lvm_config on an LVM2 subvolume with an ext4 file system, mounted at /lvm_mount, use:#
snapper -c lvm_config create-config -f "lvm(ext4)" /lvm_mount
For Btrfs:#
snapper -c config_name create-config -f btrfs /mount-point
- The
-c config_name
option specifies the name of the configuration file. - The
create-config
tells snapper to create a configuration file. - The
-f file_system
tells snapper what file system to use; if this is omitted snapper will attempt to detect the file system. - The
/mount-point
is where the subvolume or thinly-provisioned LVM2 file system is mounted.
Alternatively, to create a configuration file calledbtrfs_config
, on a Btrfs subvolume that is mounted at/btrfs_mount
, use:#
snapper -c btrfs_config create-config -f btrfs /btrfs_mount
/etc/snapper/configs/
directory.
14.2. Creating a Snapper Snapshot
- Pre Snapshot
- A pre snapshot serves as a point of origin for a post snapshot. The two are closely tied and designed to track file system modification between the two points. The pre snapshot must be created before the post snapshot.
- Post Snapshot
- A post snapshot serves as the end point to the pre snapshot. The coupled pre and post snapshots define a range for comparison. By default, every new snapper volume is configured to create a background comparison after a related post snapshot is created successfully.
- Single Snapshot
- A single snapshot is a standalone snapshot created at a specific moment. These can be used to track a timeline of modifications and have a general point to return to later.
14.2.1. Creating a Pre and Post Snapshot Pair
14.2.1.1. Creating a Pre Snapshot with Snapper
#
snapper -c config_name create -t pre
-c config_name
option creates a snapshot according to the specifications in the named configuration file. If the configuration file does not yet exist, see Section 14.1, “Creating Initial Snapper Configuration”.
create -t
option specifies what type of snapshot to create. Accepted entries are pre
, post
, or single
.
lvm_config
configuration file, as created in Section 14.1, “Creating Initial Snapper Configuration”, use:
#
snapper -c SnapperExample create -t pre -p
1
-p
option prints the number of the created snapshot and is optional.
14.2.1.2. Creating a Post Snapshot with Snapper
Procedure 14.2. Creating a Post Snapshot
- Determine the number of the pre snapshot:
#
snapper -c config_name list
For example, to display the list of snapshots created using the configuration filelvm_config
, use the following:#
snapper -c lvm_config list
Type | # | Pre # | Date | User | Cleanup | Description | Userdata -------+---+-------+-------------------+------+----------+-------------+--------- single | 0 | | | root | | current | pre | 1 | | Mon 06<...> | root | | |This output shows that the pre snapshot is number 1. - Create a post snapshot that is linked to a previously created pre snapshot:
#
snapper -c config_file create -t post --pre-num pre_snapshot_number
- The
-t post
option specifies the creation of the post snapshot type. - The
--pre-num
option specifies the corresponding pre snapshot.
For example, to create a post snapshot using thelvm_config
configuration file and is linked to pre snapshot number 1, use:#
snapper -c lvm_config create -t post --pre-num 1 -p
2The-p
option prints the number of the created snapshot and is optional. - The pre and post snapshots 1 and 2 are now created and paired. Verify this with the
list
command:#
snapper -c lvm_config list
Type | # | Pre # | Date | User | Cleanup | Description | Userdata -------+---+-------+-------------------+------+----------+-------------+--------- single | 0 | | | root | | current | pre | 1 | | Mon 06<...> | root | | | post | 2 | 1 | Mon 06<...> | root | | |
14.2.1.3. Wrapping a Command in Pre and Post Snapshots
- Running the
snapper create pre snapshot
command. - Running a command or a list of commands to perform actions with a possible impact on the file system content.
- Running the
snapper create post snapshot
command.
Procedure 14.3. Wrapping a Command in Pre and Post Snapshots
- To wrap a command in pre and post snapshots:
#
snapper -c lvm_config create --command "command_to_be_tracked"
For example, to track the creation of the/lvm_mount/hello_file
file:#
snapper -c lvm_config create --command "echo Hello > /lvm_mount/hello_file"
- To verify this, use the
status
command:#
snapper -c config_file status first_snapshot_number..second_snapshot_number
For example, to track the changes made in the first step:#
snapper -c lvm_config status 3..4
+..... /lvm_mount/hello_fileUse thelist
command to verify the number of the snapshot if needed.For more information on thestatus
command, see Section 14.3, “Tracking Changes Between Snapper Snapshots”.
14.2.2. Creating a Single Snapper Snapshot
-t
option specifies single. The single snapshot is used to create a single snapshot in time without having it relate to any others. However, if you are interested in a straightforward way to create snapshots of LVM2 thin volumes without the need to automatically generate comparisons or list additional information, Red Hat recommends using the System Storage Manager instead of Snapper for this purpose, as described in Section 16.2.6, “Snapshot”.
#
snapper -c config_name create -t single
lvm_config
configuration file.
#
snapper -c lvm_config create -t single
snapper diff
, xadiff
, and status
commands to compare any two snapshots. For more information on these commands, see Section 14.3, “Tracking Changes Between Snapper Snapshots”.
14.2.3. Configuring Snapper to Take Automated Snapshots
- 10 hourly snapshots, and the final hourly snapshot is saved as a “daily” snapshot.
- 10 daily snapshots, and the final daily snapshot for a month is saved as a “monthly” snapshot.
- 10 monthly snapshots, and the final monthly snapshot is saved as a “yearly” snapshot.
- 10 yearly snapshots.
/etc/snapper/config-templates/default
file. When you use the snapper create-config
command to create a configuration, any unspecified values are set based on the default configuration. You can edit the configuration for any defined volume in the /etc/snapper/configs/config_name
file.
14.3. Tracking Changes Between Snapper Snapshots
status
, diff
, and xadiff
commands to track the changes made to a subvolume between snapshots:
- status
- The
status
command shows a list of files and directories that have been created, modified, or deleted between two snapshots, that is a comprehensive list of changes between two snapshots. You can use this command to get an overview of the changes without excessive details.For more information, see Section 14.3.1, “Comparing Changes with thestatus
Command”. - diff
- The
diff
command shows a diff of modified files and directories between two snapshots as received from thestatus
command if there is at least one modification detected.For more information, see Section 14.3.2, “Comparing Changes with thediff
Command”. - xadiff
- The
xadiff
command compares how the extended attributes of a file or directory have changed between two snapshots.For more information, see Section 14.3.3, “Comparing Changes with thexadiff
Command”.
14.3.1. Comparing Changes with the status
Command
status
command shows a list of files and directories that have been created, modified, or deleted between two snapshots.
#
snapper -c config_file status first_snapshot_number..second_snapshot_number
list
command to determine snapshot numbers if needed.
lvm_config
.
#
snapper -c lvm_config status 1..2
tp.... /lvm_mount/dir1 -..... /lvm_mount/dir1/file_a c.ug.. /lvm_mount/file2 +..... /lvm_mount/file3 ....x. /lvm_mount/file4 cp..xa /lvm_mount/file5
+..... /lvm_mount/file3 |||||| 123456
Output | Meaning |
---|---|
. | Nothing has changed. |
+ | File created. |
- | File deleted. |
c | Content changed. |
t | The type of directory entry has changed. For example, a former symbolic link has changed to a regular file with the same file name. |
Output | Meaning |
---|---|
. | No permissions changed. |
p | Permissions changed. |
Output | Meaning |
---|---|
. | No user ownership changed. |
u | User ownership has changed. |
Output | Meaning |
---|---|
. | No group ownership changed. |
g | Group ownership has changed. |
Output | Meaning |
---|---|
. | No extended attributes changed. |
x | Extended attributes changed. |
Output | Meaning |
---|---|
. | No ACLs changed. |
a | ACLs modified. |
14.3.2. Comparing Changes with the diff
Command
diff
command shows the changes of modified files and directories between two snapshots.
#
snapper -c config_name diff first_snapshot_number..second_snapshot_number
list
command to determine the number of the snapshot if needed.
lvm_config
configuration file, use:
#
snapper -c lvm_config diff 1..2
--- /lvm_mount/.snapshots/13/snapshot/file4 19<...> +++ /lvm_mount/.snapshots/14/snapshot/file4 20<...> @@ -0,0 +1 @@ +words
file4
had been modified to add "words" into the file.
14.3.3. Comparing Changes with the xadiff
Command
xadiff
command compares how the extended attributes of a file or directory have changed between two snapshots:
#
snapper -c config_name xadiff first_snapshot_number..second_snapshot_number
list
command to determine the number of the snapshot if needed.
lvm_config
configuration file, use:
#
snapper -c lvm_config xadiff 1..2
14.4. Reversing Changes in Between Snapshots
undochange
command in the following format, where 1
is the first snapshot and 2
is the second snapshot:
snapper -c config_name undochange 1..2
Important
undochange
command does not revert the Snapper volume back to its original state and does not provide data consistency. Any file modification that occurs outside of the specified range, for example after snapshot 2, will remain unchanged after reverting back, for example to the state of snapshot 1. For example, if undochange
is run to undo the creation of a user, any files owned by that user can still remain.
undochange
command is used.
undochange
command with the root file system, as doing so is likely to lead to a failure.
undochange
command works:
Figure 14.1. Snapper Status over Time
snapshot_1
is created, file_a
is created, then file_b
deleted. Snapshot_2
is then created, after which file_a
is edited and file_c
is created. This is now the current state of the system. The current system has an edited version of file_a
, no file_b
, and a newly created file_c
.
undochange
command is called, Snapper generates a list of modified files between the first listed snapshot and the second. In the diagram, if you use the snapper -c SnapperExample undochange 1..2
command, Snapper creates a list of modified files (that is, file_a
is created; file_b
is deleted) and applies them to the current system. Therefore:
- the current system will not have
file_a
, as it has yet to be created whensnapshot_1
was created. file_b
will exist, copied fromsnapshot_1
into the current system.file_c
will exist, as its creation was outside the specified time.
file_b
and file_c
conflict, the system can become corrupted.
snapper -c SnapperExample undochange 2..1
command. In this case, the current system replaces the edited version of file_a
with one copied from snapshot_1
, which undoes edits of that file made after snapshot_2
was created.
Using the mount and unmount Commands to Reverse Changes
undochange
command is not always the best way to revert modifications. With the status
and diff
command, you can make a qualified decision, and use the mount
and unmount
commands instead of Snapper. The mount
and unmount
commands are only useful if you want to mount snapshots and browse their content independently of Snapper workflow.
mount
command activates respective LVM Snapper snapshot before mounting. Use the mount
and unmount
commands if you are, for example, interested in mounting snapshots and extracting older version of several files manually. To revert files manually, copy them from a mounted snapshot to the current file system. The current file system, snapshot 0, is the live file system created in Procedure 14.1, “Creating a Snapper Configuration File”. Copy the files to the subtree of the original /mount-point.
mount
and unmount
commands for explicit client-side requests. The /etc/snapper/configs/config_name
file contains the ALLOW_USERS= and ALLOW_GROUPS= variables where you can add users and groups. Then, snapperd
allows you to perform mount operations for the added users and groups.
14.5. Deleting a Snapper Snapshot
#
snapper -c config_name delete snapshot_number
list
command to verify that the snapshot was successfully deleted.
Chapter 15. Swap Space
Amount of RAM in the system | Recommended swap space | Recommended swap space if allowing for hibernation |
---|---|---|
⩽ 2 GB | 2 times the amount of RAM | 3 times the amount of RAM |
> 2 GB – 8 GB | Equal to the amount of RAM | 2 times the amount of RAM |
> 8 GB – 64 GB | At least 4 GB | 1.5 times the amount of RAM |
> 64 GB | At least 4 GB | Hibernation not recommended |
Note
Important
free
and cat /proc/swaps
commands to verify how much and where swap is in use.
rescue
mode, see Booting Your Computer in Rescue Mode in the Red Hat Enterprise Linux 7 Installation Guide. When prompted to mount the file system, select .
15.1. Adding Swap Space
15.1.1. Extending Swap on an LVM2 Logical Volume
/dev/VolGroup00/LogVol01
is the volume you want to extend by 2 GB):
Procedure 15.1. Extending Swap on an LVM2 Logical Volume
- Disable swapping for the associated logical volume:
#
swapoff -v /dev/VolGroup00/LogVol01
- Resize the LVM2 logical volume by 2 GB:
#
lvresize /dev/VolGroup00/LogVol01 -L +2G
- Format the new swap space:
#
mkswap /dev/VolGroup00/LogVol01
- Enable the extended logical volume:
#
swapon -v /dev/VolGroup00/LogVol01
- To test if the swap logical volume was successfully extended and activated, inspect active swap space:
$
cat /proc/swaps
$free -h
15.1.2. Creating an LVM2 Logical Volume for Swap
/dev/VolGroup00/LogVol02
is the swap volume you want to add:
- Create the LVM2 logical volume of size 2 GB:
#
lvcreate VolGroup00 -n LogVol02 -L 2G
- Format the new swap space:
#
mkswap /dev/VolGroup00/LogVol02
- Add the following entry to the
/etc/fstab
file:/dev/VolGroup00/LogVol02 swap swap defaults 0 0
- Regenerate mount units so that your system registers the new configuration:
#
systemctl daemon-reload
- Activate swap on the logical volume:
#
swapon -v /dev/VolGroup00/LogVol02
- To test if the swap logical volume was successfully created and activated, inspect active swap space:
$
cat /proc/swaps
$free -h
15.1.3. Creating a Swap File
Procedure 15.2. Add a Swap File
- Determine the size of the new swap file in megabytes and multiply by 1024 to determine the number of blocks. For example, the block size of a 64 MB swap file is 65536.
- Create an empty file:
#
dd if=/dev/zero of=/swapfile bs=1024 count=65536
Replace count with the value equal to the desired block size. - Set up the swap file with the command:
#
mkswap /swapfile
- Change the security of the swap file so it is not world readable.
#
chmod 0600 /swapfile
- To enable the swap file at boot time, edit
/etc/fstab
as root to include the following entry:/swapfile swap swap defaults 0 0
The next time the system boots, it activates the new swap file. - Regenerate mount units so that your system registers the new
/etc/fstab
configuration:#
systemctl daemon-reload
- To activate the swap file immediately:
#
swapon /swapfile
- To test if the new swap file was successfully created and activated, inspect active swap space:
$
cat /proc/swaps
$free -h
15.2. Removing Swap Space
15.2.1. Reducing Swap on an LVM2 Logical Volume
/dev/VolGroup00/LogVol01
is the volume you want to reduce):
Procedure 15.3. Reducing an LVM2 Swap Logical Volume
- Disable swapping for the associated logical volume:
#
swapoff -v /dev/VolGroup00/LogVol01
- Reduce the LVM2 logical volume by 512 MB:
#
lvreduce /dev/VolGroup00/LogVol01 -L -512M
- Format the new swap space:
#
mkswap /dev/VolGroup00/LogVol01
- Activate swap on the logical volume:
#
swapon -v /dev/VolGroup00/LogVol01
- To test if the swap logical volume was successfully reduced, inspect active swap space:
$
cat /proc/swaps
$free -h
15.2.2. Removing an LVM2 Logical Volume for Swap
/dev/VolGroup00/LogVol02
is the swap volume you want to remove):
Procedure 15.4. Remove a Swap Volume Group
- Disable swapping for the associated logical volume:
#
swapoff -v /dev/VolGroup00/LogVol02
- Remove the LVM2 logical volume:
#
lvremove /dev/VolGroup00/LogVol02
- Remove the following associated entry from the
/etc/fstab
file:/dev/VolGroup00/LogVol02 swap swap defaults 0 0
- Regenerate mount units so that your system registers the new configuration:
#
systemctl daemon-reload
- Remove all references to the removed swap storage from the
/etc/default/grub
file:#
vi /etc/default/grub
- Rebuild the grub configuration:
- on BIOS-based machines, run:
#
grub2-mkconfig -o /boot/grub2/grub.cfg
- on UEFI-based machines, run:
#
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
- To test if the logical volume was successfully removed, inspect active swap space:
$
cat /proc/swaps
$free -h
15.2.3. Removing a Swap File
Procedure 15.5. Remove a Swap File
- At a shell prompt, execute the following command to disable the swap file (where
/swapfile
is the swap file):#
swapoff -v /swapfile
- Remove its entry from the
/etc/fstab
file. - Regenerate mount units so that your system registers the new configuration:
#
systemctl daemon-reload
- Remove the actual file:
#
rm /swapfile
15.3. Moving Swap Space
- Removing swap space Section 15.2, “Removing Swap Space”.
- Adding swap space Section 15.1, “Adding Swap Space”.
Chapter 16. System Storage Manager (SSM)
16.1. SSM Back Ends
ssmlib/main.py
which complies with the device, pool, and volume abstraction, ignoring the specifics of the underlying technology. Back ends can be registered in ssmlib/main.py
to handle specific storage technology methods, such as create
, snapshot
, or to remove
volumes and pools.
16.1.1. Btrfs Back End
Note
16.1.1.1. Btrfs Pool
btrfs_pool
.
btrfs_device_base_name
.
16.1.1.2. Btrfs Volume
/dev/lvm_pool/lvol001
. Every object in this path must exist in order for the volume to be created. Volumes can also be referenced with its mount point.
16.1.1.3. Btrfs Snapshot
16.1.1.4. Btrfs Device
16.1.2. LVM Back End
16.1.2.1. LVM Pool
lvm_pool
.
16.1.2.2. LVM Volume
16.1.2.3. LVM Snapshot
snapshot
volume is created which can then be handled just like any other LVM volume. Unlike Btrfs, LVM is able to distinguish snapshots from regular volumes so there is no need for a snapshot name to match a particular pattern.
16.1.2.4. LVM Device
16.1.3. Crypt Back End
cryptsetup
and dm-crypt target
to manage encrypted volumes. Crypt back ends can be used as a regular back end for creating encrypted volumes on top of regular block devices (or on other volumes such as LVM or MD volumes), or to create encrypted LVM volumes in a single steps.
16.1.3.1. Crypt Volume
dm-crypt
and represent the data on the original encrypted device in an unencrypted form. It does not support RAID or any device concatenation.
man cryptsetup
.
16.1.3.2. Crypt Snapshot
cryptsetup
.
16.1.4. Multiple Devices (MD) Back End
16.2. Common SSM Tasks
16.2.1. Installing SSM
# yum install system-storage-manager
- The LVM back end requires the
lvm2
package. - The Btrfs back end requires the
btrfs-progs
package. - The Crypt back end requires the
device-mapper
andcryptsetup
packages.
16.2.2. Displaying Information about All Detected Devices
list
command. The ssm list
command with no options display the following output:
#
ssm list
---------------------------------------------------------- Device Free Used Total Pool Mount point ---------------------------------------------------------- /dev/sda 2.00 GB PARTITIONED /dev/sda1 47.83 MB /test /dev/vda 15.00 GB PARTITIONED /dev/vda1 500.00 MB /boot /dev/vda2 0.00 KB 14.51 GB 14.51 GB rhel ---------------------------------------------------------- ------------------------------------------------ Pool Type Devices Free Used Total ------------------------------------------------ rhel lvm 1 0.00 KB 14.51 GB 14.51 GB ------------------------------------------------ --------------------------------------------------------------------------------- Volume Pool Volume size FS FS size Free Type Mount point --------------------------------------------------------------------------------- /dev/rhel/root rhel 13.53 GB xfs 13.52 GB 9.64 GB linear / /dev/rhel/swap rhel 1000.00 MB linear /dev/sda1 47.83 MB xfs 44.50 MB 44.41 MB part /test /dev/vda1 500.00 MB xfs 496.67 MB 403.56 MB part /boot ---------------------------------------------------------------------------------
ssm list --help
command.
Note
- Running the
devices
ordev
argument omits some devices. CDRoms and DM/MD devices, for example, are intentionally hidden as they are listed as volumes. - Some back ends do not support snapshots and cannot distinguish between a snapshot and a regular volume. Running the
snapshot
argument on one of these back ends cause SSM to attempt to recognize the volume name in order to identify a snapshot. If the SSM regular expression does not match the snapshot pattern then the snapshot is not be recognized. - With the exception of the main Btrfs volume (the file system itself), any unmounted Btrfs volumes are not shown.
16.2.3. Creating a New Pool, Logical Volume, and File System
/dev/vdb
and /dev/vdc
, a logical volume of 1G, and an XFS file system.
ssm create --fs xfs -s 1G /dev/vdb /dev/vdc
. The following options are used:
- The
--fs
option specifies the required file system type. Current supported file system types are:- ext3
- ext4
- xfs
- btrfs
- The
-s
specifies the size of the logical volume. The following suffixes are supported to define units:K
ork
for kilobytesM
orm
for megabytesG
org
for gigabytesT
ort
for terabytesP
orp
for petabytesE
ore
for exabytes
- Additionaly, with the
-s
option, the new size can be specified as a percentage. Look at the examples:10%
for 10 percent of the total pool size10%FREE
for 10 percent of the free pool space10%USED
for 10 percent of the used pool space
/dev/vdb
and /dev/vdc
, are the two devices you wish to create.
#
ssm create --fs xfs -s 1G /dev/vdb /dev/vdc
Physical volume "/dev/vdb" successfully created Physical volume "/dev/vdc" successfully created Volume group "lvm_pool" successfully created Logical volume "lvol001" created
ssm command
that may be useful. The first is the -p pool
command. This specifies the pool the volume is to be created on. If it does not yet exist, then SSM creates it. This was omitted in the given example which caused SSM to use the default name lvm_pool
. However, to use a specific name to fit in with any existing naming conventions, the -p
option should be used.
-n name
command. This names the newly created logical volume. As with the -p
, this is needed in order to use a specific name to fit in with any existing naming conventions.
#
ssm create --fs xfs -p new_pool -n XFS_Volume /dev/vdd
Volume group "new_pool" successfully created Logical volume "XFS_Volume" created
16.2.4. Checking a File System's Consistency
ssm check
command checks the file system consistency on the volume. It is possible to specify multiple volumes to check. If there is no file system on the volume, then the volume is skipped.
lvol001
, run the command ssm check /dev/lvm_pool/lvol001
.
#
ssm check /dev/lvm_pool/lvol001
Checking xfs file system on '/dev/mapper/lvm_pool-lvol001'. Phase 1 - find and verify superblock... Phase 2 - using internal log - scan filesystem freespace and inode maps... - found root inode chunk Phase 3 - for each AG... - scan (but don't clear) agi unlinked lists... - process known inodes and perform inode discovery... - agno = 0 - agno = 1 - agno = 2 - agno = 3 - agno = 4 - agno = 5 - agno = 6 - process newly discovered inodes... Phase 4 - check for duplicate blocks... - setting up duplicate extent list... - check for inodes claiming duplicate blocks... - agno = 0 - agno = 1 - agno = 2 - agno = 3 - agno = 4 - agno = 5 - agno = 6 No modify flag set, skipping phase 5 Phase 6 - check inode connectivity... - traversing filesystem ... - traversal finished ... - moving disconnected inodes to lost+found ... Phase 7 - verify link counts... No modify flag set, skipping filesystem flush and exiting.
16.2.5. Increasing a Volume's Size
ssm resize
command changes the size of the specified volume and file system. If there is no file system then only the volume itself will be resized.
/dev/vdb
that is 900MB called lvol001
.
#
ssm list
----------------------------------------------------------------- Device Free Used Total Pool Mount point ----------------------------------------------------------------- /dev/vda 15.00 GB PARTITIONED /dev/vda1 500.00 MB /boot /dev/vda2 0.00 KB 14.51 GB 14.51 GB rhel /dev/vdb 120.00 MB 900.00 MB 1.00 GB lvm_pool /dev/vdc 1.00 GB ----------------------------------------------------------------- --------------------------------------------------------- Pool Type Devices Free Used Total --------------------------------------------------------- lvm_pool lvm 1 120.00 MB 900.00 MB 1020.00 MB rhel lvm 1 0.00 KB 14.51 GB 14.51 GB --------------------------------------------------------- -------------------------------------------------------------------------------------------- Volume Pool Volume size FS FS size Free Type Mount point -------------------------------------------------------------------------------------------- /dev/rhel/root rhel 13.53 GB xfs 13.52 GB 9.64 GB linear / /dev/rhel/swap rhel 1000.00 MB linear /dev/lvm_pool/lvol001 lvm_pool 900.00 MB xfs 896.67 MB 896.54 MB linear /dev/vda1 500.00 MB xfs 496.67 MB 403.56 MB part /boot --------------------------------------------------------------------------------------------
~]# ssm resize -s +500M /dev/lvm_pool/lvol001 /dev/vdc Physical volume "/dev/vdc" successfully created Volume group "lvm_pool" successfully extended Phase 1 - find and verify superblock... Phase 2 - using internal log - scan filesystem freespace and inode maps... - found root inode chunk Phase 3 - for each AG... - scan (but don't clear) agi unlinked lists... - process known inodes and perform inode discovery... - agno = 0 - agno = 1 - agno = 2 - agno = 3 - process newly discovered inodes... Phase 4 - check for duplicate blocks... - setting up duplicate extent list... - check for inodes claiming duplicate blocks... - agno = 0 - agno = 1 - agno = 2 - agno = 3 No modify flag set, skipping phase 5 Phase 6 - check inode connectivity... - traversing filesystem ... - traversal finished ... - moving disconnected inodes to lost+found ... Phase 7 - verify link counts... No modify flag set, skipping filesystem flush and exiting. Extending logical volume lvol001 to 1.37 GiB Logical volume lvol001 successfully resized meta-data=/dev/mapper/lvm_pool-lvol001 isize=256 agcount=4, agsize=57600 blks = sectsz=512 attr=2, projid32bit=1 = crc=0 data = bsize=4096 blocks=230400, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0 ftype=0 log =internal bsize=4096 blocks=853, version=2 = sectsz=512 sunit=0 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0 data blocks changed from 230400 to 358400
ssm list
command.
#
ssm list
------------------------------------------------------------------ Device Free Used Total Pool Mount point ------------------------------------------------------------------ /dev/vda 15.00 GB PARTITIONED /dev/vda1 500.00 MB /boot /dev/vda2 0.00 KB 14.51 GB 14.51 GB rhel /dev/vdb 0.00 KB 1020.00 MB 1.00 GB lvm_pool /dev/vdc 640.00 MB 380.00 MB 1.00 GB lvm_pool ------------------------------------------------------------------ ------------------------------------------------------ Pool Type Devices Free Used Total ------------------------------------------------------ lvm_pool lvm 2 640.00 MB 1.37 GB 1.99 GB rhel lvm 1 0.00 KB 14.51 GB 14.51 GB ------------------------------------------------------ ---------------------------------------------------------------------------------------------- Volume Pool Volume size FS FS size Free Type Mount point ---------------------------------------------------------------------------------------------- /dev/rhel/root rhel 13.53 GB xfs 13.52 GB 9.64 GB linear / /dev/rhel/swap rhel 1000.00 MB linear /dev/lvm_pool/lvol001 lvm_pool 1.37 GB xfs 1.36 GB 1.36 GB linear /dev/vda1 500.00 MB xfs 496.67 MB 403.56 MB part /boot ----------------------------------------------------------------------------------------------
Note
-
instead of a +
. For example, to decrease the size of an LVM volume by 50M the command would be:
#
ssm resize -s-50M /dev/lvm_pool/lvol002
Rounding size to boundary between physical extents: 972.00 MiB WARNING: Reducing active logical volume to 972.00 MiB THIS MAY DESTROY YOUR DATA (filesystem etc.) Do you really want to reduce lvol002? [y/n]: y Reducing logical volume lvol002 to 972.00 MiB Logical volume lvol002 successfully resized
+
or -
, the value is taken as absolute.
16.2.6. Snapshot
ssm snapshot
command.
Note
lvol001
, use the following command:
#
ssm snapshot /dev/lvm_pool/lvol001
Logical volume "snap20150519T130900" created
ssm list
, and note the extra snapshot section.
#
ssm list
---------------------------------------------------------------- Device Free Used Total Pool Mount point ---------------------------------------------------------------- /dev/vda 15.00 GB PARTITIONED /dev/vda1 500.00 MB /boot /dev/vda2 0.00 KB 14.51 GB 14.51 GB rhel /dev/vdb 0.00 KB 1020.00 MB 1.00 GB lvm_pool /dev/vdc 1.00 GB ---------------------------------------------------------------- -------------------------------------------------------- Pool Type Devices Free Used Total -------------------------------------------------------- lvm_pool lvm 1 0.00 KB 1020.00 MB 1020.00 MB rhel lvm 1 0.00 KB 14.51 GB 14.51 GB -------------------------------------------------------- ---------------------------------------------------------------------------------------------- Volume Pool Volume size FS FS size Free Type Mount point ---------------------------------------------------------------------------------------------- /dev/rhel/root rhel 13.53 GB xfs 13.52 GB 9.64 GB linear / /dev/rhel/swap rhel 1000.00 MB linear /dev/lvm_pool/lvol001 lvm_pool 900.00 MB xfs 896.67 MB 896.54 MB linear /dev/vda1 500.00 MB xfs 496.67 MB 403.56 MB part /boot ---------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------- Snapshot Origin Pool Volume size Size Type ---------------------------------------------------------------------------------- /dev/lvm_pool/snap20150519T130900 lvol001 lvm_pool 120.00 MB 0.00 KB linear ----------------------------------------------------------------------------------
16.2.7. Removing an Item
ssm remove
is used to remove an item, either a device, pool, or volume.
Note
-f
argument.
-f
argument.
lvm_pool
and everything within it use the following command:
#
ssm remove lvm_pool
Do you really want to remove volume group "lvm_pool" containing 2 logical volumes? [y/n]: y Do you really want to remove active logical volume snap20150519T130900? [y/n]: y Logical volume "snap20150519T130900" successfully removed Do you really want to remove active logical volume lvol001? [y/n]: y Logical volume "lvol001" successfully removed Volume group "lvm_pool" successfully removed
16.3. SSM Resources
- The
man ssm
page provides good descriptions and examples, as well as details on all of the commands and options too specific to be documented here. - Local documentation for SSM is stored in the
doc/
directory. - The SSM wiki can be accessed at http://storagemanager.sourceforge.net/index.html.
- The mailing list can be subscribed from https://lists.sourceforge.net/lists/listinfo/storagemanager-devel and mailing list archives from http://sourceforge.net/mailarchive/forum.php?forum_name=storagemanager-devel. The mailing list is where developers communicate. There is currently no user mailing list so feel free to post questions there as well.
Chapter 17. Disk Quotas
quota
RPM must be installed to implement disk quotas.
Note
17.1. Configuring Disk Quotas
- Enable quotas per file system by modifying the
/etc/fstab
file. - Remount the file system(s).
- Create the quota database files and generate the disk usage table.
- Assign quota policies.
17.1.1. Enabling Quotas
Procedure 17.1. Enabling Quotas
- Log in as root.
- Edit the
/etc/fstab
file. - Add either the
usrquota
orgrpquota
or both options to the file systems that require quotas.
Example 17.1. Edit /etc/fstab
vim
type the following:
#
vim /etc/fstab
Example 17.2. Add Quotas
/dev/VolGroup00/LogVol00 / ext3 defaults 1 1 LABEL=/boot /boot ext3 defaults 1 2 none /dev/pts devpts gid=5,mode=620 0 0 none /dev/shm tmpfs defaults 0 0 none /proc proc defaults 0 0 none /sys sysfs defaults 0 0 /dev/VolGroup00/LogVol02 /home ext3 defaults,usrquota,grpquota 1 2 /dev/VolGroup00/LogVol01 swap swap defaults 0 0 . . .
/home
file system has both user and group quotas enabled.
Note
/home
partition was created during the installation of Red Hat Enterprise Linux. The root (/
) partition can be used for setting quota policies in the /etc/fstab
file.
17.1.2. Remounting the File Systems
usrquota
or grpquota
or both options, remount each file system whose fstab
entry has been modified. If the file system is not in use by any process, use one of the following methods:
- Run the
umount
command followed by themount
command to remount the file system. See theman
page for bothumount
andmount
for the specific syntax for mounting and unmounting various file system types. - Run the
mount -o remount file-system
command (wherefile-system
is the name of the file system) to remount the file system. For example, to remount the/home
file system, run themount -o remount /home
command.
17.1.3. Creating the Quota Database Files
quotacheck
command.
quotacheck
command examines quota-enabled file systems and builds a table of the current disk usage per file system. The table is then used to update the operating system's copy of disk usage. In addition, the file system's disk quota files are updated.
Note
quotacheck
command has no effect on XFS as the table of disk usage is completed automatically at mount time. See the man page xfs_quota(8)
for more information.
Procedure 17.2. Creating the Quota Database Files
- Create the quota files on the file system using the following command:
#
quotacheck -cug /file system
- Generate the table of current disk usage per file system using the following command:
#
quotacheck -avug
- c
- Specifies that the quota files should be created for each file system with quotas enable.
- u
- Checks for user quotas.
- g
- Checks for group quotas. If only
-g
is specified, only the group quota file is created.
-u
or -g
options are specified, only the user quota file is created.
- a
- Check all quota-enabled, locally-mounted file systems
- v
- Display verbose status information as the quota check proceeds
- u
- Check user disk quota information
- g
- Check group disk quota information
quotacheck
has finished running, the quota files corresponding to the enabled quotas (either user or group or both) are populated with data for each quota-enabled locally-mounted file system such as /home
.
17.1.4. Assigning Quotas per User
edquota
command.
- User must exist prior to setting the user quota.
Procedure 17.3. Assigning Quotas per User
- To assign the quota for a user, use the following command:
#
edquota username
Replace username with the user to which you want to assign the quotas. - To verify that the quota for the user has been set, use the following command:
#
quota username
Example 17.3. Assigning Quotas to a user
/etc/fstab
for the /home
partition (/dev/VolGroup00/LogVol02
in the following example) and the command edquota testuser
is executed, the following is shown in the editor configured as the default for the system:
Disk quotas for user testuser (uid 501): Filesystem blocks soft hard inodes soft hard /dev/VolGroup00/LogVol02 440436 0 0 37418 0 0
Note
EDITOR
environment variable is used by edquota
. To change the editor, set the EDITOR
environment variable in your ~/.bash_profile
file to the full path of the editor of your choice.
inodes
column shows how many inodes the user is currently using. The last two columns are used to set the soft and hard inode limits for the user on the file system.
Example 17.4. Change Desired Limits
Disk quotas for user testuser (uid 501): Filesystem blocks soft hard inodes soft hard /dev/VolGroup00/LogVol02 440436 500000 550000 37418 0 0
#
quota testuser
Disk quotas for user username (uid 501): Filesystem blocks quota limit grace files quota limit grace /dev/sdb 1000* 1000 1000 0 0 0
17.1.5. Assigning Quotas per Group
- Group must exist prior to setting the group quota.
Procedure 17.4. Assigning Quotas per Group
- To set a group quota, use the following command:
#
edquota -g groupname
- To verify that the group quota is set, use the following command:
#
quota -g groupname
Example 17.5. Assigning quotas to group
devel
group, use the command:
#
edquota -g devel
Disk quotas for group devel (gid 505): Filesystem blocks soft hard inodes soft hard /dev/VolGroup00/LogVol02 440400 0 0 37418 0 0
#
quota -g devel
17.1.6. Setting the Grace Period for Soft Limits
#
edquota -t
Important
edquota
commands operate on quotas for a particular user or group, the -t
option operates on every file system with quotas enabled.
17.2. Managing Disk Quotas
17.2.1. Enabling and Disabling
#
quotaoff -vaug
-u
or -g
options are specified, only the user quotas are disabled. If only -g
is specified, only group quotas are disabled. The -v
switch causes verbose status information to display as the command executes.
#
quotaon
#
quotaon -vaug
-u
or -g
options are specified, only the user quotas are enabled. If only -g
is specified, only group quotas are enabled.
/home
, use the following command:
#
quotaon -vug /home
Note
quotaon
command is not always needed for XFS because it is performed automatically at mount time. Refer to the man page quotaon(8)
for more information.
17.2.2. Reporting on Disk Quotas
repquota
utility.
Example 17.6. Output of the repquota
Command
repquota /home
produces this output:
*** Report for user quotas on device /dev/mapper/VolGroup00-LogVol02 Block grace time: 7days; Inode grace time: 7days Block limits File limits User used soft hard grace used soft hard grace ---------------------------------------------------------------------- root -- 36 0 0 4 0 0 kristin -- 540 0 0 125 0 0 testuser -- 440400 500000 550000 37418 0 0
-a
) quota-enabled file systems, use the command:
# repquota -a
--
displayed after each user is a quick way to determine whether the block or inode limits have been exceeded. If either soft limit is exceeded, a +
appears in place of the corresponding -
; the first -
represents the block limit, and the second represents the inode limit.
grace
columns are normally blank. If a soft limit has been exceeded, the column contains a time specification equal to the amount of time remaining on the grace period. If the grace period has expired, none
appears in its place.
17.2.3. Keeping Quotas Accurate
#
quotacheck
quotacheck
can be run on a regular basis, even if the system has not crashed. Safe methods for periodically running quotacheck
include:
- Ensuring quotacheck runs on next reboot
Note
This method works best for (busy) multiuser systems which are periodically rebooted.Save a shell script into the/etc/cron.daily/
or/etc/cron.weekly/
directory or schedule one using the following command:#
crontab -e
Thecrontab -e
command contains thetouch /forcequotacheck
command. This creates an emptyforcequotacheck
file in the root directory, which the system init script looks for at boot time. If it is found, the init script runsquotacheck
. Afterward, the init script removes the/forcequotacheck
file; thus, scheduling this file to be created periodically withcron
ensures thatquotacheck
is run during the next reboot.For more information aboutcron
, seeman cron
.- Running quotacheck in single user mode
- An alternative way to safely run
quotacheck
is to boot the system into single-user mode to prevent the possibility of data corruption in quota files and run the following commands:#
quotaoff -vug /file_system
#
quotacheck -vug /file_system
#
quotaon -vug /file_system
- Running quotacheck on a running system
- If necessary, it is possible to run
quotacheck
on a machine during a time when no users are logged in, and thus have no open files on the file system being checked. Run the commandquotacheck -vug file_system
; this command will fail ifquotacheck
cannot remount the given file_system as read-only. Note that, following the check, the file system will be remounted read-write.Warning
Runningquotacheck
on a live file system mounted read-write is not recommended due to the possibility of quota file corruption.
man cron
for more information about configuring cron
.
Chapter 18. Redundant Array of Independent Disks (RAID)
- Enhances speed
- Increases storage capacity using a single virtual disk
- Minimizes data loss from disk failure
18.1. RAID Types
Firmware RAID
Hardware RAID
Software RAID
- Multithreaded design
- Portability of arrays between Linux machines without reconstruction
- Backgrounded array reconstruction using idle system resources
- Hot-swappable drive support
- Automatic CPU detection to take advantage of certain CPU features such as streaming SIMD support
- Automatic correction of bad sectors on disks in an array
- Regular consistency checks of RAID data to ensure the health of the array
- Proactive monitoring of arrays with email alerts sent to a designated email address on important events
- Write-intent bitmaps which drastically increase the speed of resync events by allowing the kernel to know precisely which portions of a disk need to be resynced instead of having to resync the entire array
- Resync checkpointing so that if you reboot your computer during a resync, at startup the resync will pick up where it left off and not start all over again
- The ability to change parameters of the array after installation. For example, you can grow a 4-disk RAID5 array to a 5-disk RAID5 array when you have a new disk to add. This grow operation is done live and does not require you to reinstall on the new array.
18.2. RAID Levels and Linear Support
- Level 0
- RAID level 0, often called "striping," is a performance-oriented striped data mapping technique. This means the data being written to the array is broken down into strips and written across the member disks of the array, allowing high I/O performance at low inherent cost but provides no redundancy.Many RAID level 0 implementations will only stripe the data across the member devices up to the size of the smallest device in the array. This means that if you have multiple devices with slightly different sizes, each device will get treated as though it is the same size as the smallest drive. Therefore, the common storage capacity of a level 0 array is equal to the capacity of the smallest member disk in a Hardware RAID or the capacity of smallest member partition in a Software RAID multiplied by the number of disks or partitions in the array.
- Level 1
- RAID level 1, or "mirroring," has been used longer than any other form of RAID. Level 1 provides redundancy by writing identical data to each member disk of the array, leaving a "mirrored" copy on each disk. Mirroring remains popular due to its simplicity and high level of data availability. Level 1 operates with two or more disks, and provides very good data reliability and improves performance for read-intensive applications but at a relatively high cost. [3]The storage capacity of the level 1 array is equal to the capacity of the smallest mirrored hard disk in a Hardware RAID or the smallest mirrored partition in a Software RAID. Level 1 redundancy is the highest possible among all RAID types, with the array being able to operate with only a single disk present.
- Level 4
- Level 4 uses parity [4] concentrated on a single disk drive to protect data. Because the dedicated parity disk represents an inherent bottleneck on all write transactions to the RAID array, level 4 is seldom used without accompanying technologies such as write-back caching, or in specific circumstances where the system administrator is intentionally designing the software RAID device with this bottleneck in mind (such as an array that will have little to no write transactions once the array is populated with data). RAID level 4 is so rarely used that it is not available as an option in Anaconda. However, it could be created manually by the user if truly needed.The storage capacity of Hardware RAID level 4 is equal to the capacity of the smallest member partition multiplied by the number of partitions minus one. Performance of a RAID level 4 array will always be asymmetrical, meaning reads will outperform writes. This is because writes consume extra CPU and main memory bandwidth when generating parity, and then also consume extra bus bandwidth when writing the actual data to disks because you are writing not only the data, but also the parity. Reads need only read the data and not the parity unless the array is in a degraded state. As a result, reads generate less traffic to the drives and across the busses of the computer for the same amount of data transfer under normal operating conditions.
- Level 5
- This is the most common type of RAID. By distributing parity across all of an array's member disk drives, RAID level 5 eliminates the write bottleneck inherent in level 4. The only performance bottleneck is the parity calculation process itself. With modern CPUs and Software RAID, that is usually not a bottleneck at all since modern CPUs can generate parity very fast. However, if you have a sufficiently large number of member devices in a software RAID5 array such that the combined aggregate data transfer speed across all devices is high enough, then this bottleneck can start to come into play.As with level 4, level 5 has asymmetrical performance, with reads substantially outperforming writes. The storage capacity of RAID level 5 is calculated the same way as with level 4.
- Level 6
- This is a common level of RAID when data redundancy and preservation, and not performance, are the paramount concerns, but where the space inefficiency of level 1 is not acceptable. Level 6 uses a complex parity scheme to be able to recover from the loss of any two drives in the array. This complex parity scheme creates a significantly higher CPU burden on software RAID devices and also imposes an increased burden during write transactions. As such, level 6 is considerably more asymmetrical in performance than levels 4 and 5.The total capacity of a RAID level 6 array is calculated similarly to RAID level 5 and 4, except that you must subtract 2 devices (instead of 1) from the device count for the extra parity storage space.
- Level 10
- This RAID level attempts to combine the performance advantages of level 0 with the redundancy of level 1. It also helps to alleviate some of the space wasted in level 1 arrays with more than 2 devices. With level 10, it is possible to create a 3-drive array configured to store only 2 copies of each piece of data, which then allows the overall array size to be 1.5 times the size of the smallest devices instead of only equal to the smallest device (like it would be with a 3-device, level 1 array).The number of options available when creating level 10 arrays as well as the complexity of selecting the right options for a specific use case make it impractical to create during installation. It is possible to create one manually using the command line
mdadm
tool. For more information on the options and their respective performance trade-offs, seeman md
. - Linear RAID
- Linear RAID is a grouping of drives to create a larger virtual drive. In linear RAID, the chunks are allocated sequentially from one member drive, going to the next drive only when the first is completely filled. This grouping provides no performance benefit, as it is unlikely that any I/O operations split between member drives. Linear RAID also offers no redundancy and decreases reliability; if any one member drive fails, the entire array cannot be used. The capacity is the total of all member disks.
18.3. Linux RAID Subsystems
Linux Hardware RAID Controller Drivers
mdraid
mdraid
subsystem was designed as a software RAID solution for Linux; it is also the preferred solution for software RAID under Linux. This subsystem uses its own metadata format, generally referred to as native mdraid
metadata.
mdraid
also supports other metadata formats, known as external metadata. Red Hat Enterprise Linux 7 uses mdraid
with external metadata to access ISW / IMSM (Intel firmware RAID) sets. mdraid
sets are configured and controlled through the mdadm
utility.
dmraid
dmraid
tool is used on a wide variety of firmware RAID implementations. dmraid
also supports Intel firmware RAID, although Red Hat Enterprise Linux 7 uses mdraid
to access Intel firmware RAID sets.
Note
dmraid
has been deprecated since the Red Hat Enterprise Linux 7.5 release. It will be removed in a future major release of Red Hat Enterprise Linux. For more information, see Deprecated Functionality in the Red Hat Enterprise Linux 7.5 Release Notes.
18.4. RAID Support in the Anaconda Installer
mdraid
, and can recognize existing mdraid
sets.
initrd
which RAID set(s) to activate before searching for the root file system.
18.5. Converting Root Disk to RAID1 after Installation
- Copy the contents of the PowerPC Reference Platform (PReP) boot partition from
/dev/sda1
to/dev/sdb1
:#
dd if=/dev/sda1 of=/dev/sdb1
- Update the Prep and boot flag on the first partition on both disks:
$
parted /dev/sda set 1 prep on
$
parted /dev/sda set 1 boot on
$
parted /dev/sdb set 1 prep on
$
parted /dev/sdb set 1 boot on
Note
grub2-install /dev/sda
command does not work on a PowerPC machine and returns an error, but the system boots as expected.
18.6. Configuring RAID Sets
mdadm
mdadm
command-line tool is used to manage software RAID in Linux, i.e. mdraid
. For information on the different mdadm
modes and options, see man mdadm
. The man
page also contains useful examples for common operations like creating, monitoring, and assembling software RAID arrays.
dmraid
dmraid
is used to manage device-mapper RAID sets. The dmraid
tool finds ATARAID devices using multiple metadata format handlers, each supporting various formats. For a complete list of supported formats, run dmraid -l
.
dmraid
tool cannot configure RAID sets after creation. For more information about using dmraid
, see man dmraid
.
18.7. Creating Advanced RAID Devices
/boot
or root file system arrays on a complex RAID device; in such cases, you may need to use array options that are not supported by Anaconda. To work around this, perform the following procedure:
Procedure 18.1. Creating Advanced RAID Devices
- Insert the install disk.
- During the initial boot up, select Rescue mode, the user will be presented with a command line terminal.instead of or . When the system fully boots into
- From this terminal, use
parted
to create RAID partitions on the target hard drives. Then, usemdadm
to manually create raid arrays from those partitions using any and all settings and options available. For more information on how to do these, see Chapter 13, Partitions,man parted
, andman mdadm
. - Once the arrays are created, you can optionally create file systems on the arrays as well.
- Reboot the computer and this time select Anaconda searches the disks in the system, it will find the pre-existing RAID devices.or to install as normal. As
- When asked about how to use the disks in the system, selectand click . In the device listing, the pre-existing MD RAID devices will be listed.
- Select a RAID device, click Anaconda will perform the install to this pre-existing RAID device, preserving the custom options you selected when you created it in Rescue Mode.and configure its mount point and (optionally) the type of file system it should use (if you did not create one earlier) then click .
Note
man
pages. Both the man mdadm
and man md
contain useful information for creating custom RAID arrays, and may be needed throughout the workaround. As such, it can be helpful to either have access to a machine with these man
pages present, or to print them out prior to booting into Rescue Mode and creating your custom arrays.
Chapter 19. Using the mount
Command
mount
or umount
command respectively. This chapter describes the basic use of these commands, as well as some advanced topics, such as moving a mount point or creating shared subtrees.
19.1. Listing Currently Mounted File Systems
$
mount
device on directory type type (options)
findmnt
utility, which allows users to list mounted file systems in a tree-like form, is also available from Red Hat Enterprise Linux 6.1. To display all currently attached file systems, run the findmnt
command with no additional arguments:
$
findmnt
19.1.1. Specifying the File System Type
mount
command includes various virtual file systems such as sysfs
and tmpfs
. To display only the devices with a certain file system type, provide the -t
option:
$
mount -t type
findmnt
command:
$
findmnt -t type
ext4
File Systems”.
Example 19.1. Listing Currently Mounted ext4
File Systems
/
and /boot
partitions are formatted to use ext4
. To display only the mount points that use this file system, use the following command:
$
mount -t ext4
/dev/sda2 on / type ext4 (rw) /dev/sda1 on /boot type ext4 (rw)
findmnt
command, type:
$
findmnt -t ext4
TARGET SOURCE FSTYPE OPTIONS / /dev/sda2 ext4 rw,realtime,seclabel,barrier=1,data=ordered /boot /dev/sda1 ext4 rw,realtime,seclabel,barrier=1,data=ordered
19.2. Mounting a File System
mount
command in the following form:
$
mount
[option…] device directory
- a full path to a block device: for example,
/dev/sda3
- a universally unique identifier (UUID): for example,
UUID=34795a28-ca6d-4fd8-a347-73671d0c19cb
- a volume label: for example,
LABEL=home
Important
findmnt
utility with the directory as its argument and verify the exit code:
findmnt
directory;echo
$?
1
.
mount
command without all required information, that is without the device name, the target directory, or the file system type, the mount
reads the contents of the /etc/fstab
file to check if the given file system is listed. The /etc/fstab
file contains a list of device names and the directories in which the selected file systems are set to be mounted as well as the file system type and mount options. Therefore, when mounting a file system that is specified in /etc/fstab
, you can choose one of the following options:
mount
[option…] directorymount
[option…] device
root
(see Section 19.2.2, “Specifying the Mount Options”).
Note
blkid
command in the following form:
blkid
device
/dev/sda3
:
#
blkid /dev/sda3
/dev/sda3: LABEL="home" UUID="34795a28-ca6d-4fd8-a347-73671d0c19cb" TYPE="ext3"
19.2.1. Specifying the File System Type
mount
detects the file system automatically. However, there are certain file systems, such as NFS
(Network File System) or CIFS
(Common Internet File System), that are not recognized, and need to be specified manually. To specify the file system type, use the mount
command in the following form:
$
mount -t type device directory
mount
command. For a complete list of all available file system types, see the section called “Manual Page Documentation”.
Type | Description |
---|---|
ext2 | The ext2 file system. |
ext3 | The ext3 file system. |
ext4 | The ext4 file system. |
btrfs | The btrfs file system. |
xfs | The xfs file system. |
iso9660 | The ISO 9660 file system. It is commonly used by optical media, typically CDs. |
nfs | The NFS file system. It is commonly used to access files over the network. |
nfs4 | The NFSv4 file system. It is commonly used to access files over the network. |
udf | The UDF file system. It is commonly used by optical media, typically DVDs. |
vfat | The FAT file system. It is commonly used on machines that are running the Windows operating system, and on certain digital media such as USB flash drives or floppy disks. |
Example 19.2. Mounting a USB Flash Drive
/dev/sdc1
device and that the /media/flashdisk/
directory exists, mount it to this directory by typing the following at a shell prompt as root
:
~]# mount -t vfat /dev/sdc1 /media/flashdisk
19.2.2. Specifying the Mount Options
mount
-o
options device directory
mount
interprets incorrectly the values following spaces as additional parameters.
Option | Description |
---|---|
async | Allows the asynchronous input/output operations on the file system. |
auto | Allows the file system to be mounted automatically using the mount -a command. |
defaults | Provides an alias for async,auto,dev,exec,nouser,rw,suid . |
exec | Allows the execution of binary files on the particular file system. |
loop | Mounts an image as a loop device. |
noauto | Default behavior disallows the automatic mount of the file system using the mount -a command. |
noexec | Disallows the execution of binary files on the particular file system. |
nouser | Disallows an ordinary user (that is, other than root ) to mount and unmount the file system. |
remount | Remounts the file system in case it is already mounted. |
ro | Mounts the file system for reading only. |
rw | Mounts the file system for both reading and writing. |
user | Allows an ordinary user (that is, other than root ) to mount and unmount the file system. |
Example 19.3. Mounting an ISO Image
/media/cdrom/
directory exists, mount the image to this directory by running the following command:
#
mount -o ro,loop Fedora-14-x86_64-Live-Desktop.iso /media/cdrom
19.2.3. Sharing Mounts
mount
command implements the --bind
option that provides a means for duplicating certain mounts. Its usage is as follows:
$
mount --bind old_directory new_directory
$
mount --rbind old_directory new_directory
- Shared Mount
- A shared mount allows the creation of an exact replica of a given mount point. When a mount point is marked as a shared mount, any mount within the original mount point is reflected in it, and vice versa. To change the type of a mount point to a shared mount, type the following at a shell prompt:
$
mount --make-shared mount_point
Alternatively, to change the mount type for the selected mount point and all mount points under it:$
mount --make-rshared mount_point
See Example 19.4, “Creating a Shared Mount Point” for an example usage. - Slave Mount
- A slave mount allows the creation of a limited duplicate of a given mount point. When a mount point is marked as a slave mount, any mount within the original mount point is reflected in it, but no mount within a slave mount is reflected in its original. To change the type of a mount point to a slave mount, type the following at a shell prompt:
mount
--make-slave
mount_pointAlternatively, it is possible to change the mount type for the selected mount point and all mount points under it by typing:mount
--make-rslave
mount_pointSee Example 19.5, “Creating a Slave Mount Point” for an example usage.Example 19.5. Creating a Slave Mount Point
This example shows how to get the content of the/media/
directory to appear in/mnt/
as well, but without any mounts in the/mnt/
directory to be reflected in/media/
. Asroot
, first mark the/media/
directory as shared:~]#
mount --bind /media /media
~]#mount --make-shared /media
Then create its duplicate in/mnt/
, but mark it as "slave":~]#
mount --bind /media /mnt
~]#mount --make-slave /mnt
Now verify that a mount within/media/
also appears in/mnt/
. For example, if the CD-ROM drive contains non-empty media and the/media/cdrom/
directory exists, run the following commands:~]#
mount /dev/cdrom /media/cdrom
~]#ls /media/cdrom
EFI GPL isolinux LiveOS ~]#ls /mnt/cdrom
EFI GPL isolinux LiveOSAlso verify that file systems mounted in the/mnt/
directory are not reflected in/media/
. For instance, if a non-empty USB flash drive that uses the/dev/sdc1
device is plugged in and the/mnt/flashdisk/
directory is present, type:~]#
mount /dev/sdc1 /mnt/flashdisk
~]#ls /media/flashdisk
~]#ls /mnt/flashdisk
en-US publican.cfg - Private Mount
- A private mount is the default type of mount, and unlike a shared or slave mount, it does not receive or forward any propagation events. To explicitly mark a mount point as a private mount, type the following at a shell prompt:
mount
--make-private
mount_pointAlternatively, it is possible to change the mount type for the selected mount point and all mount points under it:mount
--make-rprivate
mount_pointSee Example 19.6, “Creating a Private Mount Point” for an example usage.Example 19.6. Creating a Private Mount Point
Taking into account the scenario in Example 19.4, “Creating a Shared Mount Point”, assume that a shared mount point has been previously created by using the following commands asroot
:~]#
mount --bind /media /media
~]#mount --make-shared /media
~]#mount --bind /media /mnt
To mark the/mnt/
directory as private, type:~]#
mount --make-private /mnt
It is now possible to verify that none of the mounts within/media/
appears in/mnt/
. For example, if the CD-ROM drives contains non-empty media and the/media/cdrom/
directory exists, run the following commands:~]#
mount /dev/cdrom /media/cdrom
~]#ls /media/cdrom
EFI GPL isolinux LiveOS ~]#ls /mnt/cdrom
~]#It is also possible to verify that file systems mounted in the/mnt/
directory are not reflected in/media/
. For instance, if a non-empty USB flash drive that uses the/dev/sdc1
device is plugged in and the/mnt/flashdisk/
directory is present, type:~]#
mount /dev/sdc1 /mnt/flashdisk
~]#ls /media/flashdisk
~]#ls /mnt/flashdisk
en-US publican.cfg - Unbindable Mount
- In order to prevent a given mount point from being duplicated whatsoever, an unbindable mount is used. To change the type of a mount point to an unbindable mount, type the following at a shell prompt:
mount
--make-unbindable
mount_pointAlternatively, it is possible to change the mount type for the selected mount point and all mount points under it:mount
--make-runbindable
mount_pointSee Example 19.7, “Creating an Unbindable Mount Point” for an example usage.Example 19.7. Creating an Unbindable Mount Point
To prevent the/media/
directory from being shared, asroot
:#
mount --bind /media /media
#
mount --make-unbindable /media
This way, any subsequent attempt to make a duplicate of this mount fails with an error:#
mount --bind /media /mnt
mount: wrong fs type, bad option, bad superblock on /media, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so
19.2.4. Moving a Mount Point
#
mount --move old_directory new_directory
Example 19.8. Moving an Existing NFS Mount Point
/mnt/userdirs/
. As root
, move this mount point to /home
by using the following command:
#
mount --move /mnt/userdirs /home
#
ls /mnt/userdirs
#
ls /home
jill joe
19.2.5. Setting Read-only Permissions for root
19.2.5.1. Configuring root
to Mount with Read-only Permissions on Boot
- In the
/etc/sysconfig/readonly-root
file, changeREADONLY
toyes
:# Set to 'yes' to mount the file systems as read-only. READONLY=yes [output truncated]
- Change
defaults
toro
in the root entry (/
) in the/etc/fstab
file:/dev/mapper/luks-c376919e... / ext4 ro,x-systemd.device-timeout=0 1 1
- Add
ro
to theGRUB_CMDLINE_LINUX
directive in the/etc/default/grub
file and ensure that it does not containrw
:GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet ro"
- Recreate the GRUB2 configuration file:
#
grub2-mkconfig -o /boot/grub2/grub.cfg
- If you need to add files and directories to be mounted with write permissions in the
tmpfs
file system, create a text file in the/etc/rwtab.d/
directory and put the configuration there. For example, to mount/etc/example/file
with write permissions, add this line to the/etc/rwtab.d/example
file:files /etc/example/file
Important
Changes made to files and directories intmpfs
do not persist across boots.See Section 19.2.5.3, “Files and Directories That Retain Write Permissions” for more information on this step. - Reboot the system.
19.2.5.2. Remounting root
Instantly
/
) was mounted with read-only permissions on system boot, you can remount it with write permissions:
#
mount -o remount,rw /
/
is incorrectly mounted with read-only permissions.
/
with read-only permissions again, run:
#
mount -o remount,ro /
Note
/
with read-only permissions. A better approach is to retain write permissions for certain files and directories by copying them into RAM, as described in Section 19.2.5.1, “Configuring root
to Mount with Read-only Permissions on Boot”.
19.2.5.3. Files and Directories That Retain Write Permissions
tmpfs
temporary file system. The default set of such files and directories is read from the /etc/rwtab
file, which contains:
dirs /var/cache/man dirs /var/gdm [output truncated] empty /tmp empty /var/cache/foomatic [output truncated] files /etc/adjtime files /etc/ntp.conf [output truncated]
/etc/rwtab
file follow this format:
how the file or directory is copied to tmpfs path to the file or directory
tmpfs
in the following three ways:
empty path
: An empty path is copied totmpfs
. Example:empty /tmp
dirs path
: A directory tree is copied totmpfs
, empty. Example:dirs /var/run
files path
: A file or a directory tree is copied totmpfs
intact. Example:files /etc/resolv.conf
/etc/rwtab.d/
.
19.3. Unmounting a File System
umount
command:
$
umount
directory$
umount
device
root
, the correct permissions must be available to unmount the file system. For more information, see Section 19.2.2, “Specifying the Mount Options”. See Example 19.9, “Unmounting a CD” for an example usage.
Important
umount
command fails with an error. To determine which processes are accessing the file system, use the fuser
command in the following form:
$
fuser
-m
directory
/media/cdrom/
directory:
$
fuser -m /media/cdrom
/media/cdrom: 1793 2013 2022 2435 10532c 10672c
Example 19.9. Unmounting a CD
/media/cdrom/
directory, use the following command:
$
umount /media/cdrom
19.4. mount
Command References
Manual Page Documentation
man 8 mount
: The manual page for themount
command that provides a full documentation on its usage.man 8 umount
: The manual page for theumount
command that provides a full documentation on its usage.man 8 findmnt
: The manual page for thefindmnt
command that provides a full documentation on its usage.man 5 fstab
: The manual page providing a thorough description of the/etc/fstab
file format.
Useful Websites
- Shared subtrees — An LWN article covering the concept of shared subtrees.
Chapter 20. The volume_key
Function
volume_key
. libvolume_key is a library for manipulating storage volume encryption keys and storing them separately from volumes. volume_key
is an associated command line tool used to extract keys and passphrases in order to restore access to an encrypted hard drive.
volume_key
to back up the encryption keys before handing over the computer to the end user.
volume_key
only supports the LUKS volume encryption format.
Note
volume_key
is not included in a standard install of Red Hat Enterprise Linux 7 server. For information on installing it, refer to http://fedoraproject.org/wiki/Disk_encryption_key_escrow_use_cases.
20.1. volume_key
Commands
volume_key
is:
volume_key [OPTION]... OPERAND
volume_key
are determined by specifying one of the following options:
--save
- This command expects the operand volume [packet]. If a packet is provided then
volume_key
will extract the keys and passphrases from it. If packet is not provided, thenvolume_key
will extract the keys and passphrases from the volume, prompting the user where necessary. These keys and passphrases will then be stored in one or more output packets. --restore
- This command expects the operands volume packet. It then opens the volume and uses the keys and passphrases in the packet to make the volume accessible again, prompting the user where necessary, such as allowing the user to enter a new passphrase, for example.
--setup-volume
- This command expects the operands volume packet name. It then opens the volume and uses the keys and passphrases in the packet to set up the volume for use of the decrypted data as name.Name is the name of a dm-crypt volume. This operation makes the decrypted volume available as
/dev/mapper/name
.This operation does not permanently alter the volume by adding a new passphrase, for example. The user can access and modify the decrypted volume, modifying volume in the process. --reencrypt
,--secrets
, and--dump
- These three commands perform similar functions with varying output methods. They each require the operand packet, and each opens the packet, decrypting it where necessary.
--reencrypt
then stores the information in one or more new output packets.--secrets
outputs the keys and passphrases contained in the packet.--dump
outputs the content of the packet, though the keys and passphrases are not output by default. This can be changed by appending--with-secrets
to the command. It is also possible to only dump the unencrypted parts of the packet, if any, by using the--unencrypted
command. This does not require any passphrase or private key access.
-o
,--output packet
- This command writes the default key or passphrase to the packet. The default key or passphrase depends on the volume format. Ensure it is one that is unlikely to expire, and will allow
--restore
to restore access to the volume. --output-format format
- This command uses the specified format for all output packets. Currently, format can be one of the following:
asymmetric
: uses CMS to encrypt the whole packet, and requires a certificateasymmetric_wrap_secret_only
: wraps only the secret, or keys and passphrases, and requires a certificatepassphrase
: uses GPG to encrypt the whole packet, and requires a passphrase
--create-random-passphrase packet
- This command generates a random alphanumeric passphrase, adds it to the volume (without affecting other passphrases), and then stores this random passphrase into the packet.
20.2. Using volume_key
as an Individual User
volume_key
can be used to save encryption keys by using the following procedure.
Note
/path/to/volume
is a LUKS device, not the plaintext device contained within. blkid -s type /path/to/volume
should report type="crypto_LUKS"
.
Procedure 20.1. Using volume_key
Stand-alone
- Run:
A prompt will then appear requiring an escrow packet passphrase to protect the key.volume_key --save
/path/to/volume
-o escrow-packet - Save the generated
escrow-packet
file, ensuring that the passphrase is not forgotten.
Procedure 20.2. Restore Access to Data with Escrow Packet
- Boot the system in an environment where
volume_key
can be run and the escrow packet is available (a rescue mode, for example). - Run:
A prompt will appear for the escrow packet passphrase that was used when creating the escrow packet, and for the new passphrase for the volume.volume_key --restore
/path/to/volume
escrow-packet - Mount the volume using the chosen passphrase.
cryptsetup luksKillSlot
.
20.3. Using volume_key
in a Larger Organization
volume_key
can use asymmetric cryptography to minimize the number of people who know the password required to access encrypted data on any computer.
20.3.1. Preparation for Saving Encryption Keys
Procedure 20.3. Preparation
- Create an X509 certificate/private pair.
- Designate trusted users who are trusted not to compromise the private key. These users will be able to decrypt the escrow packets.
- Choose which systems will be used to decrypt the escrow packets. On these systems, set up an NSS database that contains the private key.If the private key was not created in an NSS database, follow these steps:
- Store the certificate and private key in an
PKCS#12
file. - Run:
certutil -d
/the/nss/directory
-NAt this point it is possible to choose an NSS database password. Each NSS database can have a different password so the designated users do not need to share a single password if a separate NSS database is used by each user. - Run:
pk12util -d
/the/nss/directory
-ithe-pkcs12-file
- Distribute the certificate to anyone installing systems or saving keys on existing systems.
- For saved private keys, prepare storage that allows them to be looked up by machine and volume. For example, this can be a simple directory with one subdirectory per machine, or a database used for other system management tasks as well.
20.3.2. Saving Encryption Keys
Note
/path/to/volume
is a LUKS device, not the plaintext device contained within; blkid -s type /path/to/volume
should report type="crypto_LUKS"
.
Procedure 20.4. Saving Encryption Keys
- Run:
volume_key --save
/path/to/volume
-c/path/to/cert
escrow-packet - Save the generated
escrow-packet
file in the prepared storage, associating it with the system and the volume.
20.3.3. Restoring Access to a Volume
Procedure 20.5. Restoring Access to a Volume
- Get the escrow packet for the volume from the packet storage and send it to one of the designated users for decryption.
- The designated user runs:
volume_key --reencrypt -d
/the/nss/directory
escrow-packet-in -o escrow-packet-outAfter providing the NSS database password, the designated user chooses a passphrase for encryptingescrow-packet-out
. This passphrase can be different every time and only protects the encryption keys while they are moved from the designated user to the target system. - Obtain the
escrow-packet-out
file and the passphrase from the designated user. - Boot the target system in an environment that can run
volume_key
and have theescrow-packet-out
file available, such as in a rescue mode. - Run:
volume_key --restore
/path/to/volume
escrow-packet-outA prompt will appear for the packet passphrase chosen by the designated user, and for a new passphrase for the volume. - Mount the volume using the chosen volume passphrase.
cryptsetup luksKillSlot
, for example, to free up the passphrase slot in the LUKS header of the encrypted volume. This is done with the command cryptsetup luksKillSlot device key-slot
. For more information and examples see cryptsetup --help
.
20.3.4. Setting up Emergency Passphrases
volume_key
can work with passphrases as well as encryption keys.
volume_key --save /path/to/volume
-c /path/to/ert
--create-random-passphrase passphrase-packet
passphrase-packet
. It is also possible to combine the --create-random-passphrase
and -o
options to generate both packets at the same time.
volume_key --secrets -d /your/nss/directory passphrase-packet
20.4. volume_key
References
volume_key
can be found:
- in the readme file located at
/usr/share/doc/volume_key-*/README
- on
volume_key
's manpage usingman volume_key
Chapter 21. Solid-State Disk Deployment Guidelines
TRIM
command for ATA, and WRITE SAME
with UNMAP
set, or UNMAP
command for SCSI).
discard
support is most useful when the following points are true:
- Free space is still available on the file system.
- Most logical blocks on the underlying storage device have already been written to.
UNMAP
, see the section 4.7.3.4 of the SCSI Block Commands 3 T10 Specification.
Note
discard
support. To determine if your solid-state device has discard
support, check for /sys/block/sda/queue/discard_granularity
, which is the size of internal allocation unit of device.
Deployment Considerations
TRIM
mechanism:
- Non-deterministic
TRIM
- Deterministic
TRIM
(DRAT) - Deterministic Read Zero after
TRIM
(RZAT)
TRIM
mechanism can cause data leakage as the read
command to the LBA after a TRIM
returns different or same data. RZAT returns zero after the read
command and Red Hat recommends this TRIM
mechanism to avoid data leakage. It is affected only in SSD. Choose the disk which supports RZAT mechanism.
TRIM
mechanism used depends on hardware implementation. To find the type of TRIM
mechanism on ATA, use the hdparm
command. See the following example to find the type of TRIM
mechanism:
#
hdparm -I /dev/sda | grep TRIM
Data Set Management TRIM supported (limit 8 block) Deterministic read data after TRIM
man hdparm
.
discard
correctly. You can set discard in the raid456.conf
file, or in the GRUB2 configuration. For instructions, see the following procedures.
Procedure 21.1. Setting discard in raid456.conf
devices_handle_discard_safely
module parameter is set in the raid456
module. To enable discard in the raid456.conf
file:
- Verify that your hardware supports discards:
#
cat /sys/block/disk-name/queue/discard_zeroes_data
If the returned value is1
, discards are supported. If the command returns0
, the RAID code has to zero the disk out, which takes more time. - Create the
/etc/modprobe.d/raid456.conf
file, and include the following line:options raid456 devices_handle_discard_safely=Y
- Use the
dracut -f
command to rebuild the initial ramdisk (initrd
). - Reboot the system for the changes to take effect.
Procedure 21.2. Setting discard in the GRUB2 Configuration
devices_handle_discard_safely
module parameter is set in the raid456
module. To enable discard in the GRUB2 configuration:
- Verify that your hardware supports discards:
#
cat /sys/block/disk-name/queue/discard_zeroes_data
If the returned value is1
, discards are supported. If the command returns0
, the RAID code has to zero the disk out, which takes more time. - Add the following line to the
/etc/default/grub
file:raid456.devices_handle_discard_safely=Y
- The location of the GRUB2 configuration file is different on systems with the BIOS firmware and on systems with UEFI. Use one of the following commands to recreate the GRUB2 configuration file.
- On a system with the BIOS firmware, use:
#
grub2-mkconfig -o /boot/grub2/grub.cfg
- On a system with the UEFI firmware, use:
#
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
- Reboot the system for the changes to take effect.
Note
discard
option of the mount
command. For example, to mount /dev/sda2
to /mnt
with discard enabled, use:
#
mount -t ext4 -o discard /dev/sda2 /mnt
discard
command to, primarily, avoid problems on devices which might not properly implement discard. The Linux swap
code issues discard
commands to discard-enabled devices, and there is no option to control this behavior.
Performance Tuning Considerations
Chapter 22. Write Barriers
fsync()
is persistent throughout a power loss.
fsync()
heavily or create and delete many small files will likely run much slower.
22.1. Importance of Write Barriers
- The file system sends the body of the transaction to the storage device.
- The file system sends a commit block.
- If the transaction and its corresponding commit block are written to disk, the file system assumes that the transaction will survive any power failure.
How Write Barriers Work
- The disk contains all the data.
- No re-ordering has occurred.
fsync()
call also issues a storage cache flush. This guarantees that file data is persistent on disk even if power loss occurs shortly after fsync()
returns.
22.2. Enabling and Disabling Write Barriers
Note
-o nobarrier
option for mount
. However, some devices do not support write barriers; such devices log an error message to /var/log/messages
. For more information, see Table 22.1, “Write Barrier Error Messages per File System”.
File System | Error Message |
---|---|
ext3/ext4 | JBD: barrier-based sync failed on device - disabling barriers |
XFS | Filesystem device - Disabling barriers, trial barrier write failed |
btrfs | btrfs: disabling barriers on dev device |
22.3. Write Barrier Considerations
Disabling Write Caches
#
hdparm -W0 /device/
Battery-Backed Write Caches
MegaCli64
tool to manage target drives. To show the state of all back-end drives for LSI Megaraid SAS, use:
#
MegaCli64 -LDGetProp -DskCache -LAll -aALL
#
MegaCli64 -LDSetProp -DisDskCache -Lall -aALL
Note
Chapter 23. Storage I/O Alignment and Size
parted
, lvm
, mkfs.*
, and the like) to optimize data placement and access. If a legacy device does not export I/O alignment and size data, then storage management tools in Red Hat Enterprise Linux 7 will conservatively align I/O on a 4k (or larger power of 2) boundary. This will ensure that 4k-sector devices operate correctly even if they do not indicate any required/preferred I/O alignment and size.
23.1. Parameters for Storage Access
- physical_block_size
- Smallest internal unit on which the device can operate
- logical_block_size
- Used externally to address a location on the device
- alignment_offset
- The number of bytes that the beginning of the Linux block device (partition/MD/LVM device) is offset from the underlying physical alignment
- minimum_io_size
- The device’s preferred minimum unit for random I/O
- optimal_io_size
- The device’s preferred unit for streaming I/O
physical_block_size
internally but expose a more granular 512-byte logical_block_size
to Linux. This discrepancy introduces potential for misaligned I/O. To address this, the Red Hat Enterprise Linux 7 I/O stack will attempt to start all data areas on a naturally-aligned boundary (physical_block_size
) by making sure it accounts for any alignment_offset if the beginning of the block device is offset from the underlying physical alignment.
minimum_io_size
) and streaming I/O (optimal_io_size
) of a device. For example, minimum_io_size
and optimal_io_size
may correspond to a RAID device's chunk size and stripe size respectively.
23.2. Userspace Access
logical_block_size
boundary, and in multiples of the logical_block_size
.
logical_block_size
is 4K) it is now critical that applications perform direct I/O in multiples of the device's logical_block_size
. This means that applications will fail with native 4k devices that perform 512-byte aligned I/O rather than 4k-aligned I/O.
sysfs
and block device ioctl
interfaces.
man libblkid
. This man
page is provided by the libblkid-devel
package.
sysfs Interface
- /sys/block/
disk
/alignment_offsetor/sys/block/disk
/partition
/alignment_offsetNote
The file location depends on whether the disk is a physical disk (be that a local disk, local RAID, or a multipath LUN) or a virtual disk. The first file location is applicable to physical disks while the second file location is applicable to virtual disks. The reason for this is because virtio-blk will always report an alignment value for the partition. Physical disks may or may not report an alignment value. - /sys/block/
disk
/queue/physical_block_size - /sys/block/
disk
/queue/logical_block_size - /sys/block/
disk
/queue/minimum_io_size - /sys/block/
disk
/queue/optimal_io_size
sysfs
attributes for "legacy" devices that do not provide I/O parameters information, for example:
Example 23.1. sysfs
Interface
alignment_offset: 0 physical_block_size: 512 logical_block_size: 512 minimum_io_size: 512 optimal_io_size: 0
23.3. I/O Standards
ATA
IDENTIFY DEVICE
command. ATA devices only report I/O parameters for physical_block_size
, logical_block_size
, and alignment_offset
. The additional I/O hints are outside the scope of the ATA Command Set.
SCSI
BLOCK LIMITS VPD
page) and READ CAPACITY(16)
command to devices which claim compliance with SPC-3.
READ CAPACITY(16)
command provides the block sizes and alignment offset:
LOGICAL BLOCK LENGTH IN BYTES
is used to derive/sys/block/disk/queue/physical_block_size
LOGICAL BLOCKS PER PHYSICAL BLOCK EXPONENT
is used to derive/sys/block/disk/queue/logical_block_size