Snappy rolling back on kernel panic

8 May 2015

Image you get an update and the kernel panics with that update, what are you to do? Suppose now that you have a snappy based system, this is automatically solved for you.

Here’s a short video showing this on a Beagle Bone Black, the concept is quite simple, if there is a panic, we revert to the last known state. In this video I inject an initrd that panics on boot after issuing a snappy update and before rebooting into the update.

In this video you observe the following:

  • Manually checking for updates.
  • Manually applying the updates.
  • How the a/b boot selection is done.
  • Implicitly observe the internal (subject to change) layout of snappy-boot and system-a or system-b selection.
  • Rebooting into the new kernel.
  • Observing a panic and rebooting back into the working system.

In the normal case this would seldom happen (the broken boot aside) as the autopiloting feature is enabled by default today, which you can check by running snappy config ubuntu-core