28 Feb 09 Local and Remote Kernel Upgrades – Failsafe Grub

Grub (and LILO too for that matter) has a useful ‘failsafe’ feature that can be configured. This proves especially useful for remote kernel upgrades, where a failed boot will render your machine offline and unavailable.

Here is my standard grub config. I have just added my new 2.6.28 kernel.

Firstly, I will change my ‘default 0′ to ‘default 1′ to ensure that the default booted kernel is the current good working one. Then I will make set panic=5 on the new kernel to ensure that if it does fail, the system reboots automatically after 5 seconds. My new configuration is now:

One edited, I can now set the default just once on the next boot to be entry ’0′ which is the new kernel:

At this point, the default kernel on my next reboot will be my new kernel. Should it panic however, the system will reboot after 5 seconds into my regular default kernel which is my good working kernel.

Upon rebooting, use ‘uname -a’ to check which kernel is running. Should it be your new one, you can set that to your default. If your old one reappears, then the new kernel caused a panic and needs work.

Bear in mind that this will prevent a kernel panic situation only. Should your new kernel not contain network device drivers for example, it will still likely boot successfully, just without bringing a network interface up, which will lock you out of your machine.

You could set a timer on boot in one of the boot scripts or as a cron job that will test for such a situation and reboot, or automatically reboot within ‘x’ minutes unless you’ve successfully logged in to kill the timer.

Tags: 2.6.18, 2.6.28, boot, color, debian, default, failsafe, grub, initrd, kernel, kernel panic, kernel upgrade, network interface, panic, reboot, root, title, uname

Reader's Comments

1. Simon Carr | 17 Apr 2009 6:28 pm

   Thanks! I was looking for this. I know how to do it in LILO (and that shows how out of date I am with kernel compiles )

2. c0rnoTa | 17 Jul 2009 12:14 pm

   Thx! I Was looking for this too !

3. pcz | 15 Feb 2010 11:26 pm

   you should clearly state, what versions of GRUB have this functionality.
   0.96, 0.97 or newer?

   maybe some distros have they own versions patched with this functionality?

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