How to switch to a generic kernel in a headless Ubuntu Server 12.04?

Question

I just got a dedicated server with Ubuntu 12.04 installed with a custom compiled kernel. Since I would like to install VirtualBox and this custom kernel doesn't support dynamic module loading (for security) I need to change the kernel.

I'm running some Ubuntu servers for years but never played with grub and a headless computer.

When the command update-grub is run it shows the different kernel it finds. Here is what I see

Generating grub.cfg ...
Found linux image: /boot/bzImage-3.2.13-xxxx-grs-ipv6-64
Found linux image: /boot/vmlinuz-3.2.0-34-generic
Found initrd image: /boot/initrd.img-3.2.0-34-generic
  No volume groups found
done

The first one is the active one as seen with uname -r. To me it looks like the second kernel is the one I should use. But I don't know how to configure grub2 to use it.

The computer is also configured with a software RAID using mdadm I guess. Never used that before. I don't know if playing with the grub of changing kernel could brake this.

What must I do to set the generic kernel as the default one so that I can get VirtualBox running.

Solution

To change the default menu entry from a terminal:

1. Obtain the existing menuentry choice number (starting from 0) run the following from the terminal: grep menuentry /boot/grub/grub.cfg
2. Now open /etc/default/grub as root then update GRUB_DEFAULT to the corresponding menuentry number.
3. Run sudo update-grub
4. Reboot !

Comments

[chmike]

Perfect. It rebooted and uname -r returns 3.2.0-34-generic. Thank you very much.

[Chef Pharaoh]

This does not work for me since the first page in the boot menu consists of: Ubuntu, Advanced Options (where all my kernel versions are), Mem test, Mem test. So if I change to default of 2 then the Mem test runs instead of the kernel I want from the Advanced menu.