Restart to new kernel w/o changing bootloader? [SOLVED]

petlab · Last edited by petlab on Fri Mar 18, 2005 9:38 pm; edited 1 time in total

I want to try a new kernel remotely. I know that it may panic. If this happens, I want the computer to restart, and boot into the default, good kernel.

How can I "reboot" to a new kernel without starting from the bootloader? I want to boot the new kernel, while running. No settings need to be saved. From there, it would restart completely. It would be like a "warm reboot", starting at the point right after the bootloader loads the kernel.

I figured I would set my hardware watchdog for 5 minutes, then jump into the new kernel. If it panics, the watchdog will reset the computer, and the default, good kernel would load from the untouched grub.conf.

Any help where to look for this? It is like "remote development" of a server. Trying new kerns that may panic, without having to edit my bootloader script (grub.conf)

Thanks.
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KsE · Posted: Fri Mar 18, 2005 9:16 pm Post subject:

If you're at the terminal, you can put it as the second on your list. When grub starts, select the second one. Then if it reboots, it'll load of the first one, which will be your good one.

Don't know how you could do that remotely though.

adaptr · Posted: Fri Mar 18, 2005 9:23 pm Post subject:

The short answer is that you can't, unless you use UML or a virtual machine.

Or a boot loader that lets you boot with different options exactly once and then reverts back.

I don't know if one exists that can...
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petlab · Posted: Fri Mar 18, 2005 9:24 pm Post subject:

https://www.redhat.com/archives/fedora-devel-list/2004-January/msg00270.html
'lilo -R' sets a one time default before you shutdown. That allows remote testing where you don't have access to the console at boot. If the kernel fails it can be rebooted automatically (or any lunk can hit reset) and it gets the old default next boot.

I don't want to use LILO, but this is one solution to my question.

[EDIT]GRUB VERSION available

:oops:

RTFM, me! Yes, it can be done. Reading the docs helps

There are two parts to this:
1. Configure grub right (howto forthcoming on gentoo-wiki)
2 Make your watchdog reboot the computer ??? (working on it) Or get a manual reset.
This part is not so easy, when I reboot, grub can get the job done, but in case of a
panic, hmm. using "reboot" restarts the machine, which means having the watchdog
inactive. Need to boot without resetting the watchdog.
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