Tech Tip

Tweaking Grub 2

07.11.08 | 2 Comments

A little while ago I wrote about my problems booting Linux on a Dell Optiplex 320 the solution was to install Grub 2 and tweak the boot options. Since then I have run into a couple other problems which have required me to learn a little more about managing Grub 2 on a Debian based system (Ubuntu in my case). Specifically, I want my changes to grub.cfg to persist between kernel upgrades. So here is what I have learned.


Every time a new kernel is installed, /usr/sbin/update-grub is called. This re-writes /boot/grub/grub.cfg. So any changes you make to grub.cfg directly are obliterated. However, the new grub.cfg is generated from:

  • /boot/grub/grub.cfg
  • /etc/grub.d

So if I know how to edit those files, I can make my changes persistent.

Changing default kernel options

/etc/default/grub allows you to set parameters that appear in the grub.cfg file. In my case I wanted every “linux” command to have the “acpi=off” option appended. So I added the following line to /etc/default/grub:

Now just run
sudo /usr/sbin/update-grub
and presto! All the “linux” commands have acpi=off appended.

Adding a boot option

My other problem was that everytime grub.cfg was updated, my Windows boot option was deleted. To fix that I needed to add a new file to /etc/grub.d. Read /etc/grub.d/README for more details, but the summary is:

  1. Create a file named “21_windows”
  2. Put the following code in the file:
    set -e
    cat << EOF
    menuentry "Other Operating Systems" {
    set root=(hd0,1)
    title Other Operating Systems
    }menuentry "Microsoft Windows XP Professional" {
    set root=(hd0,1)
    chainloader +1
  3. Make the file executable:
    sudo chmod 755 /etc/grub.d/21_windows
  4. Re-run
    sudo /usr/sbin/update-grub

That is all, hope it helps.


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