The following link to the Ubuntu Grub2 how to is excellent for most issues concerning Grub2 installation and modifications.
There is at least one thing that isn't correct, at least in the case of Bodhi installations, and this is when adding or changing the splash screen for Grub2.
Thanks to our forum member babel who found this inconsistency, we can deal with this easily.
As according the the link instructions, first install “grub2-splashimages” with the Synaptic Package Manager or paste this in your terminal:
sudo apt-get install grub2-splashimages
The Ubuntu link tells us to go to /etc/default/grub and change the GRUB_BACKGROUND directive to your background image.
This is not correct.
Instead do the following:
In your terminal go to /etc/grub.d/05_debian_theme:
sudo gedit /etc/grub.d/05_debian_theme
Now, find and change this line to the location of your image:
Don't forget the quotation marks!
and remember… the image HAS to be a .png, .tga or an “8 bit”.jpeg… that's “8bit”.jpeg! It also must be RGB not indexed; no .gif's.
After this you must upgrade grub in your terminal:
For other modifications, the Ubuntu link has very good information.
Here is a good Ubuntu Link on how to change the resolution of Grub on Boot. Following these directions exactly allowed the screen resolution to be set to full screen in a VM on boot.
Original wiki by Martin Thompson March 2011