Configuring LILO

LILO is a bootloader which provides a number of useful features while remaining compact. This document describes the details behind configuring the LILO bootloader.

Configuring LILO

As with any software of moderate or better complexity, configuration is required for LILO to function as desired. The configuration created by EMAC and shipped with a system will usually suffice. However, sometimes enough customization is required that the bootloader itself will need to be reconfigured. Even if custom configuration isn't required, some of this information is important for protecting against accidentally overwriting the bootloader on a developer's desktop with a bootloader that was intended for an embedded machine.

This page describes the parts of the LILO bootloader configuration file, and provides guidance on how to work with it. The other LILO pages describe how to install and use the bootloader after it has been configured.

Sections of the LILO Configuration File

The LILO configuration file is split into two sections: global and per-image. The global section, as the name implies, specifies options that pertain to LILO itself and to all images specified in the file. The per-image section specifies options that apply to a specific image, some of which may override the global options.

Shown here is the default configuration for most EMAC boards which make use of LILO:

# This tells the LILO utility where to install LILO.  This must be changed if using a desktop
# system to install LILO to a CompactFlash card.
boot=/dev/sda
map=/boot/map

lba32
# This is where the disk is found on the current system.  See the wiki for more information.
disk=/dev/sda
# This indicates that the BIOS will see this drive as the first drive.
bios=0x80
read-only
prompt
# This sets the prompt to wait for 2.5 seconds before automatically booting the first image.
# The time is specified in deciseconds.
timeout=25
vga=9
install=text
compact
# This is for lilo serial console (ttyS0,9600,8,n,1):
#serial=0,115200n8

# The following path points to the Linux kernel that LILO should boot.
image=/boot/bzImage
	root=/dev/sda1    # This is the root filesystem for the kernel to use.
	label=emac-oe
	# These are kernel commandline parameters:
	append="console=ttyS0,115200 quiet splash=silent"

Global Options

The LILO configuration file needs the following options, at a minimum, configured for the global settings:

disk This option specifies the disk to which the LILO bootloader needs to be written. This should always point to the device node currently associated with the disk. For example, when mounted on a desktop, this may be /dev/sdc, which is (usually) the third "SCSI" device connected to the system. The first would be /dev/sda, the second /dev/sdb, etc. Even though the device may not be a SCSI device, it may be mounted via a generic SCSI driver, which is why it can appear as a SCSI device. If it were mounted through the IDE subsystem instead, its device node would appear like /dev/hdc instead.
map This option specifies the location of the map file to use. Usually, this will be /boot/map.
lba32 This option tells LILO to use 32-bit Logical Block Addresses instead of cylinder/head/sector addresses. This is needed for any disk with more than 1024 cylinders. Since the vast majority of modern drives have more than 1024 cylinders, this option should always be specified.
boot This option specifies the device which contains the boot sector. As with the disk option, this should always be the device node associated with the disk on the current system. For example, boot=/dev/sdc

Additional useful options:

vga For systems which have video, this option specifies the video mode the device should use. The parameter to pass comes from the BSP (Board Support Profile) layer for the board. If unsure what to set here, EMAC can provide assistance with this.
serial This useful option specifies a serial device to which a console should be attached, as well as the configuration settings for the console. For example, to use the /dev/ttyS0 serial device (the default console port on many boards) as a serial console which communicates as 115,200 baud, 8 bits, with no stop bits: serial=0,115200n8
timeout This specifies the amount of time to wait before timing out and continuing on with the boot process using the configured defaults. This value is specified in deciseconds. For example, to set this value to 4.3 seconds: timeout=43
read-only This option tells LILO to mount the root filesystem as read-only. This is usually desired, since the Linux kernel will remount the device as writeable (if it needs to) once the boot process has been handed over to it.
install This option specifies the type of screen which will be seen when the bootloader starts. Normally, this will be set to text, which presents the simple interface shown in the examples on this page. The menu option provides a nicer way to select an image to boot, but is usually not desirable to have on an embedded machine. The bitmap option provides a graphical boot screen which looks very nice on a desktop installation, but is usually only used on an embedded machine when the product calls for showing graphics as early in the boot process as possible; a logo is typically placed here in such a case.

Per-Image Options

The following options are needed to configure images to be available to boot with LILO:

image This option specifies the location of the kernel to boot. Commonly, this will be /boot/bzImage or /boot/bzImage-custom-3.10.2
root This option specifies the root partition to mount for the image. This is typically /dev/hda1 or /dev/sda1
label This option tells LILO by what name to call the image. For instance, this is usually label=emac-oe for a standard EMAC image, but for a custom product under development, it might be label=custom-image-test-v3

Working with LILO Configurations

The above information talks about the common options and how to set them. Additional information can be found by reading through the manual page for lilo.conf. This manpage is available on many sites online.

Actually using these options to create a configuration file is done most easily by copying the EMAC provided LILO configuration file, then modifying the copy. It is a good practice to make sure a bootable flash card is set aside in case of difficulties with getting the modified flash card back into a bootable state.

Conclusion

LILO has a straightforward configuration syntax, but the details may not be immediately apparent. This documentation should fill in the missing pieces when you are configuring LILO.

Configuring LILO

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