Chapter 34. Relax-and-Recover (ReaR)
- booting a rescue system on the new hardware
- replicating the original storage layout
- restoring user and system files
rear recover
command, which starts the recovery process. During this process, ReaR replicates the partition layout and filesystems, prompts for restoring user and system files from the backup created by backup software, and finally installs the boot loader. By default, the rescue system created by ReaR only restores the storage layout and the boot loader, but not the actual user and system files.
34.1. Basic ReaR Usage
34.1.1. Installing ReaR
~]# yum install rear
34.1.2. Configuring ReaR
/etc/rear/local.conf
file. Specify the rescue system configuration by adding these lines:
OUTPUT=output format OUTPUT_URL=output location
ISO
for an ISO disk image or USB
for a bootable USB.
file:///mnt/rescue_system/
for a local filesystem directory or sftp://backup:password@192.168.0.0/
for an SFTP directory.
Example 34.1. Configuring Rescue System Format and Location
/mnt/rescue_system/
directory, add these lines to the /etc/rear/local.conf
file:
OUTPUT=ISO OUTPUT_URL=file:///mnt/rescue_system/
34.1.3. Creating a Rescue System
~]# rear -v mkrescue
Relax-and-Recover 1.17.2 / Git
Using log file: /var/log/rear/rear-rhel68.log
mkdir: created directory `/var/lib/rear/output'
Creating disk layout
Creating root filesystem layout
TIP: To login as root via ssh you need to set up /root/.ssh/authorized_keys or SSH_ROOT_PASSWORD in your configuration file
Copying files and directories
Copying binaries and libraries
Copying kernel modules
Creating initramfs
Making ISO image
Wrote ISO image: /var/lib/rear/output/rear-rhel68.iso (82M)
Copying resulting files to file location
/mnt/rescue_system/
. Because the system's host name is rhel-68
, the backup location now contains directory rhel-68/
with the rescue system and auxiliary files:
~]# ls -lh /mnt/rescue_system/rhel68/
total 82M
-rw-------. 1 root root 202 May 9 11:46 README
-rw-------. 1 root root 160K May 9 11:46 rear.log
-rw-------. 1 root root 82M May 9 11:46 rear-rhel68.iso
-rw-------. 1 root root 275 May 9 11:46 VERSION
34.1.4. Scheduling ReaR
/etc/crontab
file:
minute hour day_of_month month day_of_week root /usr/sbin/rear mkrescue
Example 34.2. Scheduling ReaR
/etc/crontab
file:
0 22 * * 1-5 root /usr/sbin/rear mkrescue
34.1.5. Performing a System Rescue
- Boot the rescue system on the new hardware. For example, burn the ISO image to a DVD and boot from the DVD.
- In the console interface, select the "Recover" option:
- You are taken to the prompt:
Figure 34.2. Rescue system: prompt
Warning
Once you have started recovery in the next step, it probably cannot be undone and you may lose anything stored on the physical disks of the system. - Run the
rear recover
command to perform the restore or migration. The rescue system then recreates the partition layout and filesystems:Figure 34.3. Rescue system: running "rear recover"
- Restore user and system files from the backup into the
/mnt/local/
directory.Example 34.3. Restoring User and System Files
In this example, the backup file is a tar archive created per instructions in Section 34.2.1.1, “Configuring the Internal Backup Method”. First, copy the archive from its storage, then unpack the files into/mnt/local/
, then delete the archive:~]#
scp root@192.168.122.6:/srv/backup/rhel68/backup.tar.gz /mnt/local/
~]#tar xf /mnt/local/backup.tar.gz -C /mnt/local/
~]#rm -f /mnt/local/backup.tar.gz
The new storage has to have enough space both for the archive and the extracted files. - Verify that the files have been restored:
~]#
ls /mnt/local/
Figure 34.4. Rescue system: restoring user and system files from the backup
- Ensure that SELinux relabels the files on the next boot:
~]#
touch /mnt/local/.autorelabel
Otherwise you may be unable to log in the system, because the/etc/passwd
file may have the incorrect SELinux context. - Finish the recovery and reboot the system:
Figure 34.5. Rescue system: finishing recovery
ReaR will then reinstall the boot loader. Upon reboot, SELinux will relabel the whole filesystem.Then you will be able to log in to the recovered system.