How do I change the default kernel that boots from GRUB?

The GRUB configuration file can be found in /boot/grub/.

[root@root /boot/grub]# ls -la grub.conf menu.lst

-rw———-
1 root
root         1037 Oct 28 11:41
grub.conf

lrwxr-xr-x
1 root
root           11
Jan 1 2003 menu.lst -> ./grub.conf

If grub.conf does not exist then simply edit menu.lst which should be a file instead of a symlink to grub.conf.

Here is an example configuration:

# grub.conf generated by anaconda

#

# Note that you do not have to rerun grub after making changes to this file

# NOTICE: You have a /boot partition. This means that

#          all kernel and initrd paths are relative to /boot/, eg.

#          root (hd0,0)

#          kernel /vmlinuz-version ro root=/dev/hda3

#          initrd /initrd-version.img

#boot=/dev/hda

default=0

timeout=10

splashimage=(hd0,0)/grub/splash.xpm.gz

title Red Hat Enterprise Linux ES (2.4.21-37.EL)

        root (hd0,0)

        kernel /vmlinuz-2.4.21-37.EL ro root=/dev/hda3

        initrd /initrd-2.4.21-37.EL.img

title Red Hat Enterprise Linux ES (2.4.21-32.0.1.EL)

        root (hd0,0)

        kernel /vmlinuz-2.4.21-32.0.1.EL ro root=/dev/hda3

        initrd /initrd-2.4.21-32.0.1.EL.img

title Red Hat Enterprise Linux ES (2.4.21-27.0.4.EL)

        root (hd0,0)

        kernel /vmlinuz-2.4.21-27.0.4.EL ro root=/dev/hda3

        initrd /initrd-2.4.21-27.0.4.EL.img

title Red Hat Enterprise Linux ES (2.4.21-27.0.2.EL)

        root (hd0,0)

        kernel /vmlinuz-2.4.21-27.0.2.EL ro root=/dev/hda3

        initrd /initrd-2.4.21-27.0.2.EL.img

The default line is the line we want to change. The first title is 0. So if I wanted title Red Hat Enterprise Linux ES (2.4.21-27.0.2.EL) to be the default kernel I would set defualt= to 4.

# grub.conf generated by anaconda

# Note that you do not have to rerun grub after making changes to this file

# NOTICE: You have a /boot partition. This means that

# all kernel and initrd paths are relative to /boot/, eg.

# root (hd0,0)

# kernel /vmlinuz-version ro root=/dev/hda3

# initrd /initrd-version.img

#boot=/dev/hda

default=4

timeout=10

splashimage=(hd0,0)/grub/splash.xpm.gz

title Red Hat Enterprise Linux ES (2.4.21-37.EL)

root (hd0,0)

kernel /vmlinuz-2.4.21-37.EL ro root=/dev/hda3

initrd /initrd-2.4.21-37.EL.img

title Red Hat Enterprise Linux ES (2.4.21-32.0.1.EL)

root (hd0,0)

kernel /vmlinuz-2.4.21-32.0.1.EL ro root=/dev/hda3

initrd /initrd-2.4.21-32.0.1.EL.img

title Red Hat Enterprise Linux ES (2.4.21-27.0.4.EL)

root (hd0,0)

kernel /vmlinuz-2.4.21-27.0.4.EL ro root=/dev/hda3

initrd /initrd-2.4.21-27.0.4.EL.img

title Red Hat Enterprise Linux ES (2.4.21-27.0.2.EL)

root (hd0,0)

kernel /vmlinuz-2.4.21-27.0.2.EL ro root=/dev/hda3

initrd /initrd-2.4.21-27.0.2.EL.img