Configuring the Boot Loader

Now that you have recompiled your kernel, you must configure the boot loader to boot the new kernel. This is a crucial step. If you do not perform this step or if you perform it incorrectly, you will not be able to boot your system. If this happens, boot your system with the boot diskette you created earlier and try configuring the boot loader again. If your boot diskette does not work, refer to Chapter 3 for more information about rescue mode.

In order to provide a redundant boot source to protect from a possible error in a new kernel, you should keep the original kernel available. During the installation of Red Hat Linux 7.3, you had the option to choose either GRUB or LILO as your boot loader. Refer to the appropriate section that follows.

GRUB

If you selected GRUB as your boot loader, modify /boot/grub/grub.conf. The default GRUB configuration file looks similar to the following:

# NOTICE:  You have a /boot partition.  This means that
#          all kernel paths are relative to /boot/
default=0
timeout=30
splashimage=(hd0,0)/grub/splash.xpm.gz

title Red Hat Linux (2.4.18-0.12)
        root (hd0,0)
        kernel /vmlinuz-2.4.18-0.12 ro root=/dev/hda3
        initrd /initrd-2.4.18-0.12.img

If you created a separate /boot partition, the paths to the kernel and initrd image are relative to the /boot partition.

To add your new kernel to GRUB, copy the existing title section to a new one and modify it to boot your new kernel image (and initrd image if you have any SCSI devices and have created an initrd image). Be sure the title of the new section is different from the title of the section to boot the old kernel. By default, Red Hat Linux uses Red Hat Linux and the kernel version in parentheses to differentiate between different kernels for GRUB to boot. In our example, the new /boot/grub/grub.conf file would look like the following:

# NOTICE:  You have a /boot partition.  This means that
#          all kernel paths are relative to /boot/
default=0
timeout=30
splashimage=(hd0,0)/grub/splash.xpm.gz

title Red Hat Linux (2.4.18-0.12-jul2001)
        root (hd0,0)
        kernel /vmlinuz-2.4.18-0.12-jul2001 ro root=/dev/hda3
        initrd /initrd-2.4.18-0.12-jul2001.img

title Red Hat Linux (2.4.18-0.12)
        root (hd0,0)
        kernel /vmlinuz-2.4.18-0.12 ro root=/dev/hda3
        initrd /initrd-2.4.18-0.12.img

The default boot entry is set to number 0. To make your new kernel the default, either place its section first or change the default entry number to the appropriate number (remember that it starts counting with 0). For GRUB, you do not need to run any commands after modifying the configuration file.

From now on, when the system boots you will see the following GRUB boot options:

Red Hat Linux (2.4.18-0.12-jul2001) 
Red Hat Linux (2.4.18-0.12)

To boot the default kernel, press [Enter] or wait for it to time out. If you want to boot the old kernel, select it and press [Enter].

You can begin testing your new kernel by rebooting your computer and watching the messages to ensure that your hardware is detected properly.

LILO

To configure LILO to boot the new kernel, you need to update the /etc/lilo.conf file and run the command /sbin/lilo -v.

The default /etc/lilo.conf file looks similar to the following:

boot=/dev/hda
map=/boot/map
install=/boot/boot.b
prompt
timeout=50
message=/boot/message
linear
default=linux

image=/boot/vmlinuz-2.4.18-0.12
	label=linux
        initrd=initrd-2.4.18-0.12.img
	read-only
	root=/dev/hda5

To add your new kernel to LILO, copy the existing image section to a new one and modify it to boot your new kernel image (and initrd image if you have any SCSI devices and have created an initrd image). Also, rename the label of the old kernel to something such as linux-old. Your /etc/lilo.conf should look similar to the following:

boot=/dev/hda
map=/boot/map
install=/boot/boot.b
prompt
timeout=50
message=/boot/message
linear
default=linux
	
image=/boot/vmlinuz-2.4.18-0.12-jul2001
label=linux
initrd=initrd-2.4.18-0.12-jul2001.img
read-only
root=/dev/hda5
		
image=/boot/vmlinuz-2.4.18-0.12
label=linux-old
initrd=initrd-2.4.18-0.12.img
read-only
root=/dev/hda5

To activate your changes, run the command /sbin/lilo -v. If all goes well, you will see output similar to the following:

LILO version 21.4-4, Copyright (C) 1992-1998 Werner Almesberger
'lba32' extensions Copyright (C) 1999,2000 John Coffman

Reading boot sector from /dev/hda
Merging with /boot/boot.b
Mapping message file /boot/message
Boot image: /boot/vmlinuz-2.4.18-0.12
Added linux *
Boot image: /boot/vmlinuz-2.4.18-0.12-jul2001
Added linux-old
Writing boot sector.

Be sure the messages contains Writing boot sector. The * after linux means that the section labeled linux is the default kernel that LILO will boot.

From now on, when the system boots you will see linux and linux-old as LILO boot options.

To boot the new kernel (linux) simply press [Enter], or wait for LILO to time out. If you want to boot the old kernel (linux-old), select linux-old and press [Enter].

You can begin testing your new kernel by rebooting your computer and watching the messages to ensure your hardware is detected properly.