How to modify boot kernel? 1

[nerbonne]

Ok, I have a dedicated server, and every time I reboot it, the kernel panicks. The thing is that I didn't do any kernel updates, but thats not the point, the point is I need to make it so it boots with the older kernels by default. Can anyone give me a quick run down on how to do that?

 

[thedaver]

Your system uses a "boot loader" to control which kernel is loaded.

Most likely your boot loader is 'grub', but could also be 'lilo' and (less likely) a few others.

Read up on grub, hunt for the config files (if it's your boot loaded) and direct the configuration to launch your desired kernel.

D.E.R. Management - IT Project Management Consulting

http://www.dermanagement.com/

 

[geirendre]

Maby if you supply more info about bootloader and what
you do to get around the "kernel panic", then we can help you better....

http://www.gnu.org/software/grub/manual/

 

[gb0mb]

If it is grub you can hit "e" to edit the grub conf. You just need to point it to the old kernel.

An alt method is to just boot a live disk and then mount /boot and do a manual edit to the conf.

Gb0mb

........99.9% User Error........

 

[nerbonne]

Ok, my bad. I wasn't very descriptive. I have a dedicated server and I have root ssh access. My boot loader is grub. I cannot modify it during boot because I don't have a console connection, and I can't use any GUI procedures (obviously).

How it has been getting fixed before is the support personnel at he NOC hook up a console and tell it to use an older kernel to boot. Unfortunately, they don't make it permanent. Why? I don't know.

Here is what support wrote to me:

-----

Dear Customer,

I placed a console to investigate and found that kernel 2.6.9-55.0.12 ELsmp was creating a kernel panic. I rebooted the server using an older kernel 2.6, 9-55. ELsmp. It is now online and responding to network requests.

Thank you,
Support

-----

I know there is a file somewhere you can edit to specify the kernel. I'm just not sure how you pick what kernel.

Thanks for the help.

 

[gb0mb]

It should be in /boot/grub/grub.conf. This is the file it looks to when booting.

Gb0mb

........99.9% User Error........

 

[geirendre]

If this is a RedHat-system,the config-file for Grub is /boot/grub/grub.conf
So what you have to do is:
1. Become root on the system. su
2. Make a backup of the original file. cp /boot/grub/grub.conf /boot/grub/grub.conf.backup
3. Open the file for editing.
4. Find the section that look something like:

title Red Hat Linux (2.6.9-55.0.12.ELsmp)
root (hd0,0)
kernel /vmlinuz-2.6.9-55.0.12.ELsmp ro root=/dev/sda1
initrd /initrd-2.6.9-55.0.12ELsmp

and replace the 2.6.9-55.0.12 ELsmp
with the right kernel 2.6.9-55.ELsmp
5. Save the file.
6. Try a reboot when you can afford some downtime,
just in case...

 

[nerbonne]

Thanks.

I changed it to:

#boot=/dev/sda
default=9
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu


Default used to be 1. I'm assuming that 1 is the first entry, and that there is no default=0, otherwise my kernel will be off one.

 

[nerbonne]

at geirendre, do you think I should change the default=9 back to 1 and use your method, or will I be ok with what I have?

Thanks

 

[geirendre]

To have multiple options and use default to choose
one of the options I think is the best solution.
That way you can test each one first and then set
that as the default option.
Default starts counting at 0, but 0 might be a header-line
in your grub menu.
grep ^title /boot/grub/grub.conf
should show you each option, starting with 0.