Boot Loader Configurations

If you are using a boot loader such as GRUB or LILO, you can configure your system to enable you to start any of your installed kernels. As seen earlier in this chapter in the section "Precautionary Steps for Modifying a Kernel of the Same Version," you can create an added entry in the boot loader configuration file for your old kernel. As you install new kernel versions, you could simply add more entries, enabling you to use any of the previous kernels. Whenever you boot, your boot loader will then present you with a list of kernels to choose from. For example, you could install a developmental version of the kernel, along with a current stable version, while keeping your old version. In the image line for each entry, you specify the filename of the kernel. You can create another boot loader entry for your older kernel.

GRUB Configurations

In the next example, the /etc/grub.conf file contains entries for two Linux kernels, one for the kernel installed earlier, 2.4.18-4, and one for a more recent kernel, 2.4.22-1. With GRUB, you only have to add a new entry for the new kernel.

# grub.conf generated by anaconda
#
#boot=/dev/hda
default=0
timeout=30
splashimage=(hd0,2)/boot/grub/splash.xpm.gz
title New Linux (2.4.22-1)
   root (hd0,2)
   kernel /boot/vmlinuz-2.4.22-1 ro root=/dev/hda3 hdc=ide-scsi
   initrd /boot/initrd-2.4.22-1.img
title  Old Linux (2.4.18-4)
   root (hd0,2)
   kernel /boot/vmlinuz-2.4.18-4 ro root=/dev/hda3 hdc=ide-scsi
   initrd /boot/initrd-2.4.18-4.img
title Windows XP
   rootnoverify (hd0,0)
   imakeactive
   chainloader +1