6.0 Technical Notes

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Red Hat Enterprise Linux 6

Technical Release Documentation

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Red Hat Enterprise Linux 6.0 Technical notes provide details on various features shipped in Red Hat Enterprise Linux 6.0, as well as all known issues of this release.

1. Installer

The Red Hat Enterprise Linux installer (also known as anaconda) assists in the installation of Red Hat Enterprise Linux 6.
Installation on systems with multipath and non-multipath storage devices
Installation of Red Hat Enterprise Linux 6 on a system with multipath and non-multipath storage devices the automatic partitioning layout in the installer may create volume groups containing a mix of multipath and non-multipath devices, thus defeating the purpose of multipath storage.
Users are advised to either select only multipath or only non-multipath devices on the disk selection screen that appears after selecting automatic partitioning. Alternatively, users can select custom partitioning.

1.1. Known Issues

  • The following issue applies to IBM Power Systems only.
    anaconda will not create a new PReP boot partition on the root disk when performing a new Red Hat Enterprise Linux 6 installation on a system that contains existing PReP Boot partitions that need to be preserved. Consequently, the Power SMS boot manager will be unable to boot the new Red Hat Enterprise Linux 6 installation. To work around this issue,
    1. Use the fdisk utility to temporarily change the partition type from type 41 'PReP Boot' to type 83 'Linux' for all existing Linux installations on the system.
    2. Perform the Red Hat Enterprise Linux 6 installation. During installation, a new PReP Boot partition will be created on the Red Hat Enterprise Linux 6 root disk.
    3. Post-installation, once the new Red Hat Enterprise Linux 6 installation is up and running, use the fdisk utility to restore all changed partition types to type 41 'PReP Boot'.
  • Anaconda now utilizes NetworkManager for network interface configuration. Consequently, kickstart users that referenced the network settings located in /tmp/netinfo must now source the ifcfg files found in /etc/sysconfig/network-scripts
  • In some circumstances, disks that contain a whole disk format (e.g. a LVM Physical Volume populating a whole disk) are not cleared correctly using the clearpart --initlabel kickstart command. Adding the --all switch — as in clearpart --initlabel --all — ensures disks are cleared correctly.
  • The nodmraid boot parameter currently cannot be used to force installation on disks containing spurious BIOS RAID metadata. To work around this issue, boot into rescue mode and run the command dmraid -rE /dev/sdX on the disks in question. Alternatively, run dd if=/dev/zero of=/dev/sdX and let it process up until the end of the disk. Note, however that this alternate procedure may take longer to complete and will erase all data on the disk.
  • Installation of Red Hat Enterprise Linux 6 on an IBM ThinkPad T43 notebook may appear to stall after choosing storage options. In these circumstances, the installer is attempting to interact with the floppy drive, and may be unresponsive for up to 30 minutes.
  • During the installation on POWER systems, the error messages similar to:
    attempt to access beyond end of device
    loop0: rw=0, want=248626, limit=248624
    may be returned to sys.log. The errors do not prevent installation and only occur during initial setup. The filesystem created by the installer will function correctly.
  • Installation on large disks (i.e. more than 2TB) on non-EFI platforms may encounter some limitations. Many BIOS systems can only boot disks that contain MSDOS partition tables, which cannot fully address large disks. A GPT partition table can address the full disk, but may not be bootable from BIOS. Consequently, the Red Hat Enterprise Linux installer does not support installing the GRUB bootloader to disks that contain GPT partition tables on non-EFI systems. When installing Red Hat Enterprise Linux 6 on a non-EFI system that contains one or more large disks, create a GPT partition table on each of the disks before proceeding to the storage configuration portion of the install process. Leaving the large disks uninitialized, or using an MSDOS partition table on them, can cause problems when creating partitions using anaconda.
  • Some Cisco UCS storage devices do not have UEFI support, which may lead to an unbootable Red Hat Enterprise Linux 6 system when installation is performed through virtual media with the system in "strict UCSM boot order rules" mode. Consequently, when installing using the UEFI method, after installation and reboot, the system will hang with a flashing cursor. To work around this issue, install the system using the BIOS install method as follows:
    1. Map the Red Hat Enterprise Linux 6 "boot.iso" file or entire OS DVD ISO using the virtual media tool
    2. Press F2 during boot to enter the BIOS setup screen
    3. Go to the "Boot Options" screen
    4. Change "UCSM boot order rules" to "Loose"
    5. Save settings and reboot
    6. Press F6 to access the boot device menu
    7. In the menu will be two options for the virtual media: "Cisco Virtual CD/DVD 1.20" and "EFI: Cisco Virtual CD/DVD 1.20 CDROM File1" select the first option to install using BIOS method. Note that only the first option will be present if using the "boot.iso" file, as it has no UEFI support.
    8. It may be necessary to re-order the devices in the BIOS Options screen after "Loose" mode has been selected in order to make the hard drive mapped to the system the first device in the boot order.
    The use of BIOS install method will effectively work around the bug, but will prevent booting from disks using a GPT partition table. This will restrict the size of disks usable as a boot disk.
  • When installing on the s390x architecture, if the installation is being performed over SSH, avoid resizing the terminal window containing the SSH session. If the terminal window is resized during installation, the installer will exit and installation will terminate.
  • Multipath storage devices with serial numbers not exactly 16 or 32 characters in length will not be detected by anaconda during installation.
  • Due to an issue with the shutdown sequence of the installer, Intel BIOS RAID sets might be left in an unclean condition post installation. Consequently, they will be rebuilt during the first boot of the system after installation. Note that this issue has no impact other than a slower first boot up after installation.
  • The installer currently does not support having the /boot volume on a logical volume. Consequently, when setting up mount points during installation, the /boot volume cannot be on an LVM volume. System z supports /boot on an LVM volume. In order to exploit this, manual configuration after installation is required. Refer to the zipl documentation for further information.
  • Minimal installations lack NetworkManager, so users wishing to have network interfaces configured for use on the first boot after installation need to make sure the network interfaces are configured and the network service is enabled at boot time. The following kickstart commands will enable eth0 for DHCP and enable the 'network' service:
    network --device eth0 --onboot yes --bootproto dhcp
    services --enabled=network
    Refer to the network device configuration documentation for more details on what the ifcfg-ethX files may contain.
  • The kernel image provided on the CD/DVD is too large for Open Firmware. Consequently, on the POWER architecture, directly booting the kernel image over a network from the CD/DVD is not possible. Instead, use yaboot to boot from a network.
  • The anaconda partition editing interface includes a button labeled Resize. Note that you can only shrink a partition with this button, not enlarge a partition.
  • System z installations cannot use the ext4 filesystem for the boot partition. The recommended alternative filesystem is ext3.
  • Channel IDs(read, write, data) for network devices are required for defining and configuring network devices on s390 systems. However, system-config-kickstart — the graphical user interface for generating a kickstart configuration — cannot define channel IDs for a network device. To work around this issue, manually edit the kickstart configuration that system-config-kickstart generates to include the desired network devices.
  • During an MPATH installation on IBM POWER 7 systems, a "DiskLabelCommit Error" might be returned. To work around this issue, first install the system in a single path configuration. Connect to the system via SSH, clear the partitions using the fdisk -l command, and delete the partitions, then exit the SSH session. Finally, continue the installation from the installer.
  • anaconda in Red Hat Enterprise Linux 6 for Power writes an incorrect value to /etc/rpm/macros that can cause issues when installing 32 and 64-bit PowerPC packages together. Users are advised to remove this file after installation.
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