LILO = LInux LOader

LInux LOader, or LILO, comes as standard on all distributions of Linux. As one of the older/oldest Linux boot loaders, its continued strong Linux community support has enabled it to evolve over time and stay viable as a usable modern-day boot loader. Some new functionality includes an enhanced user interface and exploitation of new BIOS functions that eliminate the old 1024-cylinder limit.

Although LILO continues to be developed, the basic principles of how LILO works still remain the same.

Making LILO your boot loader

If you already have a Linux distribution installed, you usually get an option to install and configure LILO (and can boot your machine into your new Linux install).

For existing Linux users migrating to LILO, first you have to acquire the latest version of LILO . As the root user, type:

# /sbin/lilo -v -v

This will use the current LILO defaults and splat anything that is currently in the MBR. note that if you want to run Windows and Linux on a single machine, you should install your Windows OS first and then the Linux OS, so that the boot loader you choose in the Linux install won't be written over by the Windows boot loader. Unlike the Linux boot loaders, the majority of Windows boot loaders will not allow you to load Linux. If you've already installed Linux first, don't fret; just create yourself a Linux boot disk so that after you have installed Windows, you can get back into your Linux install and overwrite the MBR.

Configuring LILO

LILO configuration is all done through a configuration file located in /etc/lilo.conf. Listing 1 shows an example configuration, relating to my home machine, for dual booting a Linux and Windows machine. You can visualize how this configuration relates to an actual machine by looking at my basic workstation setup:

• Primary HDD (physical disk 1) with Windows XP installed (initially all there was on the machine). In Linux terms, this HDD is /dev/hda (hd0,0 in GRUB terms).
• Secondary HDD (physical disk 2) with Red Hat Linux installed; the root partition is on the third partition of this hard drive, /dev/hdb3 (hd1,2 in GRUB terms).

Listing 1. Example lilo.conf file

boot=/dev/hda map=/boot/map install=/boot/boot.b prompt timeout=100 compact default=Linux image=/boot/vmlinuz-2.4.18-14 label=Linux root=/dev/hdb3 read-only password=linux other=/dev/hda label=WindowsXP

The options used in Listing 1 are:

• The boot= line tells LILO where to install the boot loader. In the previous example, this will install it to the MBR of first hard disk. You could alternatively install LILO in /dev/hdb3 (the Linux partition in the example), which would then require you to install another boot loader into /dev/hda that points it to the LILO boot loader; then you just let LILO act as a secondary boot loader. In general, /dev/hda is the most common place for your boot loader to reside. You can also make a LILO floppy boot disk by pointing this parameter to the floppy drive, most commonly /dev/fd0.
• map= points to the map file used by LILO internally during bootup. When you install LILO using the /sbin/lilo command, it automatically generates this file, which holds the descriptor table (among other things). My advice is to leave this as it is!
• install= is one of the files used internally by LILO during the boot process. This holds both the primary and secondary parts of the boot loader. A segment of this boot.b file is written to the MBR (the primary part of the boot loader), which then points to the map and subsequently points to the secondary boot loader. Again, leave this as it is!
• prompt= tells LILO to use the user interface (giving you in this example two selections -- Linux and WindowsXP). In addition using the prompt/user interface, you get the option to specify specific parameters for the Linux kernel or others if appropriate. If you do not specify this option in the configuration file, LILO will boot into the default OS with no user interaction and no waiting. (It's worth noting, though, that if you hold the SHIFT key down during boot, you can get the prompt up anyway, which is quite useful if you don't want the average Joe to be exposed to the boot loader).
• timeout= is the number of tenths of a second that the boot prompt will wait before automatically loading the default OS, in this case Linux. If prompt is not specified in the lilo.conf, this parameter is ignored.
• The compact option magically makes the boot process quicker by merging adjacent disk read requests into a single request. It can be a mixed blessing, though, as I've seen a number of posts on forums regarding issues with this option. This option especially useful if you wish to boot from a floppy.
• The default= option tells LILO which image to boot from by default, such as after the timeout period. This relates to a label of one of the images in the lilo.conf file. If you don't specify this option in the configuration file, it will boot the first image specified in the file.
• For each version of Linux you want to make available for users to boot into, you should specify image= and the following three options. The image option specifies the kernel version you wish to boot to.
• label= identifies the different OS you want to boot from at the user interface at runtime. In addition, this label is used for specifying the default OS to boot from. (Note: Avoid spaces in the label name; otherwise, you will get an unexpected error when loading the file.)
• The root= option tells LILO where the OS file system actually lives. In our example, it is /dev/hdb3, which is the third partition of the second disk.
• read-only tells LILO to perform the initial boot to the file system read only. Once the OS is fully booted, it is mounted read-write.
• The password= option allows you to set a password for the specific OS you are booting into. In the example this password is held in the lilo.conf file as readable text, so is easily accessible for all to read. Alternatively if you set password="" you can set the password when the bootloader is installed. These can be set on each of the operating systems you wish to boot from if required (in our example we only set a password on the Linux boot).
• other= acts like a combination of the image and root options, but for operating systems other than Linux. In our example, it tells LILO where to find the Windows OS, which resides on the first disk in the first partition. This will usually be the case if you have installed Windows first, then Linux.
• label= is the same as all other label options.

You can use many other parameters in the lilo.conf file, but the parameters in Listing 1 should get you into a fairly usable state on your machine. For further information on these and other lilo.conf parameters, refer to the manual pages (man lilo.conf). Since lilo.conf is not read at boot time, the MBR needs to be "refreshed" when this is changed. If you do not do this upon rebooting, none of your changes to lilo.conf will be reflected at startup. Like getting LILO into the MBR in the first place, you need to run:

$ /sbin/lilo -v -v

The -v -v flags give you very verbose output. There are a fair number of parameters you can specify when running LILO like we did. See the manual pages for further information (man lilo).