Kernel compilation on remote server

[Leachim]

Hi all,

I have one problem. I need to compile my new kernel on remote server. I can't go to the housing center, so I need to compile 100% working kernel. If it will not boot at startup, it can be a big problem.

Is any way, how to compile kernel, reboot the machine and when kernel will not works, it will auto reboot the pc and use the old kernel?

I hope that you understand what I need.

Ty for reply

[BradN]

Look into the following things:
program "grub-set-default" used within linux (after /boot is mounted) to set the default entry.
default command in grub.conf
fallback command in grub.conf
savedefault command in grub.conf

Use it like:
grub-set-default 0
to set the first entry to be booted

Then: make sure the "default" line in your grub.conf reads as "default saved" instead of using a number. Add a "fallback 1" line so that the backup kernel is loaded if the first kernel can't be loaded.

Next, in your first boot entry (the test kernel), put "savedefault 1" at the end of that entry such that it boots using the old kernel next time (make sure your 2nd entry is the old kernel)

Now, here's the problem. All this work ensures that the 2nd boot will start the old kernel, however we have no way of making the system reboot if it locks up or fails to start the network. You may wish to set a cron job or similar to automatically reboot the machine assuming the kernel comes up. But, if the machine locks up or something, it will need to be manually rebooted (although no intervention will be needed at the menu, which is good for a headless server).

If the kernel panics, there is a way to make it reboot automatically - add the kernel parameter "panic=1" to make it reboot after 1 second if a kernel panic occurs.

If your server has a management module that can automatically reboot the system after some delay, you should use it.

Hopefully the upgrade goes without problems - check the output of "uname -a" to find what kernel you're running. If it works fine, you'll want to alter your grub.conf to set the default to 0 and remove the savedefault line (leaving the fallback at 1 is smart in case the file becomes corrupted).

Good luck

[electronvolt]

Hi,
BradN, one slight mistake in your 'mini-HOWTO'......the command to save the default boot option in grub.conf is savedefault not setdefault

regards

[BradN]

Oops, right you are... I'll edit my previous post