Upgrades with aufs overlays

For the intrepid to jaunty upgrades exists a new experimental mode to do a test upgrade from 8.10 (intrepid) to 9.04 (jaunty) with aufs. Details https://lists.ubuntu.com/archives/ubuntu-devel/2009-March/027747.html

How it works

writable overlay into /tmp on top the systemdirs (but excluding /home) in "/" and then run the release upgrade. This way we can test easily if the system would upgrade cleanly (if no dpkg errors/maintainer script failures happen). All writes go into /tmp so after the upgrade and on the next reboot the system is back to its pre-upgraded state again (modulo /home, that is not overlayed). It also means the next boot takes a *long* time to clean /tmp - when I did test it on one of my production machines that wait made me *really* nervous But its ok, it just takes long (up to ~20 minutes or so).

Feedback is welcome, here is how to enable it:

$ sudo -s
# mkdir -p /etc/update-manager/release-upgrades.d/
# echo "[Aufs]" > /etc/update-manager/release-upgrades.d/aufs.cfg
# echo "EnableFullOverlay=yes" >> /etc/update-manager/release-upgrades.d/aufs.cfg
# exit
$ update-manager -d 
(or do-release-upgrade -d)

then follow the upgrade procedure noramlly. You will see a message dialog saying "Sandbox mode". If you don't see that, something is wrong and you need to cancel the upgrade (no worries, just hit "cancel" in the final confirmation screen). When the final confirmation screen appears, check with "mount" on a terminal if there are really "aufs" mounts. Remember to remove the file (aufs.cfg) after the next reboot if you want to perform a regular upgrade (otherwise the next run will be a sandbox upgrade again

Caveats

• it got *very little testing*, so be careful and have backups
• it does not work with the intrepid server kernel, it lacks the aufs
  • module
• the free space calculation is wrong (too small) when aufs is
  • enabled, better have plenty of free space in /tmp (~4gb for ubuntu-desktop)
• the system feels slow during the upgrade (more so than normal
  • due to aufs it seems, may also need more RAM, but I'm not sure about this yet)
• the next reboot will take *ages* (because /tmp will be cleared from
  • all the files written during the upgrade)
• there is a problem with some packages (libthunar-vfs-1-2 is one)
  • where dpkg return "Invalid cross-device link" error. it seems like its a combination of aufs/dpkg problem and currently under

    investigation: https://bugs.launchpad.net/ubuntu/+source/update-manager/+bug/342451

Feedback

• This sounds a bit like Solaris' Live Upgrade functionality. Combined with filesystems' snapshots it would be a really powerful tool. -- azrael 2009-07-10 21:54:42