Jun
29
2009

Alternating Tri-Boot for Linux Workstations

For small office/home office (SOHO) Linux workstations, I buy name-brand PCs (HP/Compaq most recently) and install Linux myself.  I’ve tried various installation strategies including Linux-only (reformatting the entire hard disk) and various forms of dual-boot or multi-boot.

Alternating tri-boot is what I call my preferred configuration for a work environment where down time or restore time due to a failed OS upgrade is costly schedule-wise.  Alternating tri-boot hosts three operating systems on a workstation: the as-delivered Windows XP partition, and two Linux distributions which both mount the same /home partition.

Description:

During normal use, two Linux distributions (e.g. openSUSE 11.0 and 10.2) and the original Microsoft OS are always bootable.  An extended partition containing four logical partitions is created. In the following diagram, the extended partition is aqua and the current Linux boot partition is the rightmost ext3 partition (labeled “root” and containing openSUSE 11.0):

Alternating Tri-boot - Two Linux OS Distros

Figure 1. Alternating Tri-boot Disk Partitions

When openSUSE 11.0 is booted, it mounts the common /home and /swap partitions and also mounts the 10.2 partition under /oldOS.  Moreover, the openSUSE 10.2 partition remains bootable since it was untouched during the installation of 11.0.  If booted as root, it would mount the same /home and swap partitions.  Thus all user data is available through normal login under either Linux OS.

Figure 2. Installation Progression for Successive Linux Versions

Figure 2. Installation Progression for Successive Linux Versions

Figure 2 shows how the contents of the partitions change as the newest Linux OS progresses from openSUSE 10.2 to 11.0 and finally 11.2.  The arrows show the new installations alternating between partitions sda6 and sda7, highlighting the point that current release is not disturbed when the next one is installed.  The availability of each release (10.2, 11.0 and 11.2) always spans two full release cycles.

Thus there are always three bootable OSes and new Linux installations alternate between the two Linux OS partitions — “alternating tri-boot”.

Benefits:

  • Never a “point of no return” during upgrades.  At any time during the installation of a new Linux distribution, you can stop and reboot into the most recent working configuration.
  • Mounting the previous distribution’s root partition under /oldOS solves  “lost configuration file” anxiety.  Ever been working on your new OS distribution for a few weeks, then fire up a seldom used application only to find out you forgot to copy/save its configuration file?  With the alternating OS partitions, that missing file is available somewhere under /oldOS.  It can be copied or diffed without having to restore from a tar file or other backup.
  • New hardware can be installed and debugged using the Windows utilities provided by the vendor.  Problems can be localized to either the hardware or the Linux driver.  No more calling the 800 number only to hear, “Load Windows and call me back.”
  • Present the machine as a Windows PC for on-site support and warranty issues.  For service calls, set the default OS back to Windows XP in the NT loader and let the technician have at it.
  • Alternating tri-boot retains the NT bootloader.  This is an integral part of avoiding point-of-no-return situations, since the original bootloader and the disk’s MBR are never overwritten or disabled during Linux installations.

Caveats:

  • In the midst of a new OS installation there is of course only one functional Linux partition.  During this window of vulnerability, you can’t fall back to booting the /oldOS partition if the current OS is damaged.  So don’t meddle with the configuration of the current OS while installing the new one.
  • Don’t let the /home partition be reformatted! Linux installer programs (e.g. YaST for openSUSE) usually scan the disks and partition tables and suggest an installation scenario.  Often they propose reformatting all of the Linux partitions.  This will wipe out the /home directories and all of your user data.  Only one partition (root) should be reformatted.

Coming soon – step-by-step instructions…

posted in opensuse, SUSE, SysAdmin by Bozzie

1 Comment to "Alternating Tri-Boot for Linux Workstations"

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