Книга: Embedded Linux Primer: A Practical, Real-World Approach

7.5.1. Lilo

7.5.1. Lilo

The Linux Loader, or Lilo, was widely used in commercial Linux distributions for desktop PC platforms; as such, it has its roots in the Intel x86/IA32 architecture. Lilo has several components. It has a primary bootstrap program that lives on the first sector of a bootable disk drive.[59] The primary loader is limited to a disk sector size, usually 512 bytes. Therefore, its primary purpose is simply to load and pass control to a secondary loader. The secondary loader can span multiple partitions and does most of the work of the bootloader.

Lilo is driven by a configuration file and utility that is part of the lilo executable. This configuration file can be read or written to only under control of the host operating system. That is, the configuration file is not referenced by the early boot code in either the primary or secondary loaders. Entries in the configuration file are read and processed by the lilo configuration utility during system installation or administration. Listing 7-10 is an example of a simple lilo.conf configuration file describing a typical dual-boot Linux and Windows installation.

Listing 7-10. Example Lilo Configuration: lilo.conf

# This is the global lilo configuration section
# These settings apply to all the "image" sections
boot = /dev/hda
timeout=50
default=linux
# This  describes the primary kernel boot image
# Lilo will display it with the label 'linux'
image=/boot/myLinux-2.6.11.1
         label=linux
         initrd=/boot/myInitrd-2.6.11.1.img
         read-only
         append="root=LABEL=/"
# This is the second OS in a dual-boot configuration
# This entry will boot a secondary image from /dev/hda1
other=/dev/hda1
         optional
         label=that_other_os

This configuration file instructs the Lilo configuration utility to use the master boot record of the first hard drive (/dev/hda). It contains a delay instruction to wait for the user to press a key before the timeout (5 seconds, in this case). This gives the system operator the choice to select from a list of OS images to boot. If the system operator presses the Tab key before the timeout, Lilo presents a list to choose from. Lilo uses the label tag as the text to display for each image.

The images are defined with the image tag in the configuration file. In the example presented in Listing 7-10, the primary (default) image is a Linux kernel image with a file name of myLinux-2.6.11.1. Lilo loads this image from the hard drive. It then loads a second file to be used as an initial ramdisk. This is the file myInitrd-2.6.11.1.img. Lilo constructs a kernel command line containing the string "root=LABEL=/" and passes this to the Linux kernel upon execution. This instructs Linux where to get its root file system after boot.

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