Purpose: Since the next generation of GRUB, GRUB2, is slowly trickling down to all major Linux distribution, I thought about writing a basic post regarding GRUB2, which discusses some of the fundamental change in GRUB2. Also the documentation on GRUB2 is not very extensive at this point of time. I am assuming that you have already upgraded to GRUB2. If you are looking for how to install splashimages in GRUB2, see this post.

To begin with, the following files and directories are important to us:

/boot/grub/grub.cfg (/boot/grub/menu.lst file in old GRUB)
/etc/default/grub
/etc/grub.d/

Also the commands:

update-grub2 (update-grub in old GRUB)
grub-mkconfig (Recommended)

are also very important if we really want to customize GRUB2 menu.

Note 1: Never edit the file/boot/grub/grub.cfg

Do not edit this file manually. Do not open the file in a text editor and start editing the entries. You might be tempted to do this but in the long run you are bound to face problems.  This file basically constructs how your GRUB2 screen looks like when you boot your system:

GRUB2_splash_image

This file is auto generated by the following command:

/usr/sbin/grub-mkconfig

and the following file:

/etc/default/grub

and templates/files from the following directory:

/etc/grub.d/

Note 2: Use grub-mkconfig instead of update-grub

For those of you who are use to using update-grub in the  legacy version of GRUB, you should use

grub-mkconfig

If you use:

update-grub2

then you will see warnings like the following:

Warning: update-grub_lib is deprecated, use grub-mkconfig_lib instead

Note 3: Partition numbering


In previous version of GRUB, we use to refer to a partition with partition number – 1. In GRUB2, we simply refer to the partition with the same number. For example, in GRUB, the following were the mappings:

/dev/hda1 - (hd0,0)
/dev/hda5 - (hd0,4)
/dev/hdb2 - (hd1,1)

However in GRUB2, the above translates to:

/dev/hda1 - (hd0,1)
/dev/hda5 - (hd0,5)
/dev/hdb2 - (hd1,2)

I personally think that it is a very good change.

Note 4: Adding a custom entry

You can add a custom boot entry in your GRUB2 menu in two ways:

Method 1:

apt-get install os-prober
os-prober
grub-mkconfig

Basically, the os-prober will detect any additional Operating Systems that are installed on your hard drive and will list them at the end. Also I think it adds the respective entries in the file:

/etc/grub.d/30_os-prober

I have not tried this method. If you do try and find problems please post it in the comment section and I will correct it.

Method 2:

Edit the file:

nano /etc/grub.d/40_custom

and add the entries like the following (example only):

#! /bin/sh -e
echo "Adding Windows" >&2
cat << EOF
menuentry "
Windows XP" {
set root=(hd0,1)
chainloader +1
}
EOF

and give the following command:

update-grub2

That’s it!

Hopefully this post has given you enough basic to start your exciting GRUB2 journey.

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