How can I write a .sh file that modifies the Ubuntu kernel boot parameters?

Question

I know that GRUB kernel boot parameters, for example panic=-1 can be added by sudo nano /etc/default/grub and then sudo update-grub.

My application comes with a setup.sh shell script that sets everything up for the user, as I want it to be able to be used by the non-technically minded user. Anyway, a driver called intel_pstate makes my app not work, so on devices where intel_pstate is detected, I want the setup.sh file to add intel_pstate=disable to the kernel boot parameters/boot line.

I really don't want to have to tell users to edit the boot parameters themselves, and am looking for a way to, in shell script code, add intel_pstate=disable to the boot parameters while maintaining the existing boot parameters.

What I've already tried

• Use this code (in a sudo bash shell):

cat /etc/default/grub > grub_bkp
echo "intel_pstate=disable" >> grub_bkp
echo gurb_bkp > /etc/default/grub

• This doesn't work, take the following /etc/default/grub file for example:

GRUB_OTHER_STUFF=1
...
GRUB_CMDLINE_LINUX_DEFAULT='panic=-1 init=/my/cool/file.sh'

• After my script is done with it, it will look like the following, not successfully applying the kernel boot parameter:

GRUB_OTHER_STUFF=1
...
GRUB_CMDLINE_LINUX_DEFAULT='panic=-1 init=/my/cool/file.sh'
intel_pstate=disable

Thank you so much for your help! :)

Answer 1

Use sed to inject a string after the search pattern GRUB_CMDLINE_LINUX_DEFAULT=':

sed -i "s/GRUB_CMDLINE_LINUX_DEFAULT='/&intel_pstate=disable /" /etc/default/grub

After that, also make sure the script updates the GRUB configuration:

update-grub

The entire script should run as root, since root is required for the above commands.