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CentOS 2.1AS







lilo.conf − configuration file for lilo


This file, by default /etc/lilo.conf, is read by the boot loader installer lilo (see lilo(8)).

It might look as follows:

boot = /dev/hda
delay = 40
vga = normal
root = /dev/hda1
image = /zImage-2.5.99
label = try
image = /zImage-1.0.9
label = 1.0.9
image = /tamu/vmlinuz

label = tamu

root = /dev/hdb2

vga = ask

other = /dev/hda3

label = dos

table = /dev/hda

This configuration file specifies that lilo uses the Master Boot Record on /dev/hda. (For a discussion of the various ways to use lilo, and the interaction with other operating systems, see user.tex from the lilo documentation.)

When booting, the boot loader will wait four seconds (40 deciseconds) for you to press Shift. If you don’t, then the first kernel image mentioned (/zImage-1.5.99, that you probably installed just five minutes ago) will be booted. If you do, the boot loader will ask you which image to boot. In case you forgot the possible choices, press [TAB] (or [?], if you have a US keyboard), and you will be presented with a menu. You now have the choice of booting this brandnew kernel, or an old trusted kernel, or a kernel on another root file system (just in case you did something stupid on your usual rootfs), or booting a different operating system. There can be up to 16 images mentioned in lilo.conf.

As can be seen above, a configuration file starts with a number of global options (the top 6 lines in the example), followed by descriptions of the options for the various images. An option in an image description will override a global option.


There are many possible keywords. The description below is almost literally from user.tex (just slightly abbreviated).

Copy the original boot sector to backup-file (which may also be a device, e.g. /dev/null) instead of /boot/boot.NNNN.


Sets the name of the device (e.g. a hard disk partition) that contains the boot sector. If this keyword is omitted, the boot sector is read from (and possibly written to) the device that is currently mounted as root.


Defines boot-time changes to partition type numbers (’hiding’). See section "Partition type change rules" of user.tex for details.


Tries to merge read requests for adjacent sectors into a single read request. This drastically reduces load time and keeps the map smaller. Using ’compact’ is especially recommended when booting from a floppy disk.


Uses the specified image as the default boot image. If ’default’ is omitted, the image appearing first in the configuration file is used.


Specifies the number of tenths of a second the boot loader should wait before booting the first image. This is useful on systems that immediately boot from the hard disk after enabling the keyboard. The boot loader doesn’t wait if ’delay’ is omitted or is set to zero.


Defines non-standard parameters for the specified disk. See section "Disk geometry" of user.tex for details. Especially useful is the ’bios=’ parameter. The BIOS numbers your disks 0x80, 0x81, etc. and it is impossible to decide which Linux disk corresponds to which BIOS disk (since this depends on the BIOS setup, and on the type of BIOS), so if you have an unusual setup you need to state the correspondence between Linux disks and BIOS disks. For example,


would say that your SCSI disk is the first BIOS disk, and your (primary master) IDE disk is the second BIOS disk.


Specifies the name of the disk parameter table. The map installer looks for /etc/disktab if ’disktab’ is omitted. The use of disktabs is discouraged.


This allows lilo to adjust 3D addresses in partition tables. Each partition entry contains a 3D (sector/head/cylinder) and a linear address of the first and the last sector of the partition. If a partition is not track-aligned and if certain other operating systems (e.g. PC/MS-DOS or OS/2) are using the same disk, they may change the 3D address. lilo can store its boot sector only on partitions where both address types correspond. lilo re-adjusts incorrect 3D start addresses if ’fix-table’ is set.

WARNING: This does not guarantee that other operating systems may not attempt to reset the address later. It is also possible that this change has other, unexpected side-effects. The correct fix is to re-partition the drive with a program that does align partitions to tracks. Also, with some disks (e.g. some large EIDE disks with address translation enabled), under some circumstances, it may even be unavoidable to have conflicting partition table entries.


Like ’backup’, but overwrite an old backup copy if it exists.


tells lilo to ignore corrupt partition tables.


Install the specified file as the new boot sector. If ’install’ is omitted, /boot/boot.b is used as the default.


Generate linear sector addresses instead of sector/head/cylinder addresses. Linear addresses are translated at run time and do not depend on disk geometry. Note that boot disks may not be portable if ’linear’ is used, because the BIOS service to determine the disk geometry does not work reliably for floppy disks. When using ’linear’ with large disks, /sbin/lilo may generate references to inaccessible disk areas, because 3D sector addresses are not known before boot time.


Generate 32-bit Logical Block Addresses instead of sector/head/cylinder addresses. If the BIOS supports packet addressing, then packet calls will be used to access the disk. This allows booting from any partition on disks greater than 8.4Gb, the translated geometry limit for C:H:S addressing. If the BIOS does not support packet addressing, then ’lba32’ addresses are translated to C:H:S, just as for ’linear’. Using ’lba32’, all floppy disk references are retained in C:H:S form.


Enables automatic recording of boot command lines as the defaults for the following boots. This way, lilo "locks" on a choice until it is manually overridden.


Specifies the location of the map file. If ’map’ is omitted, the file /boot/map is used.


specifies a file containing a message that is displayed before the boot prompt. No message is displayed while waiting for a shifting key after printing "LILO ". In the message, the FF character ([Ctrl L]) clears the local screen. The size of the message file is limited to 65535 bytes. The map file has to be rebuilt if the message file is changed or moved.


Disables warnings about possible future dangers.


The per-image option ’optional’ (see below) applies to all images.


The per-image option ’password=...’ (see below) applies to all images.


forces entering the boot prompt without expecting any prior key-presses. Unattended reboots are impossible if ’prompt’ is set and ’timeout’ isn’t.


The per-image option ’restricted’ (see below) applies to all images.


enables control from a serial line. The specified serial port is initialized and the boot loader is accepting input from it and from the PC’s keyboard. Sending a break on the serial line corresponds to pressing a shift key on the console in order to get the boot loader’s attention. All boot images should be password-protected if the serial access is less secure than access to the console, e.g. if the line is connected to a modem. The parameter string has the following syntax:


<port>: the number of the serial port, zero-based. 0 corresponds to COM1 alias /dev/ttyS0, etc. All four ports can be used (if present).

<bps>: the baud rate of the serial port. The following baud rates are supported: 110, 150, 300, 600, 1200, 2400, 4800 and 9600 bps. Default is 2400 bps.

<parity>: the parity used on the serial line. The boot loader ignores input parity and strips the 8th bit. The following (upper or lower case) characters are used to describe the parity: n for no parity, e for even parity and o for odd parity.

<bits>: the number of bits in a character. Only 7 and 8 bits are supported. Default is 8 if parity is "none", 7 if parity is "even" or "odd".

If ’serial’ is set, the value of ’delay’ is automatically raised to 20.

Example: serial=0,2400n8 initializes COM1 with the default parameters.


sets a timeout (in tenths of a second) for keyboard input. If no key is pressed for the specified time, the first image is automatically booted. Similarly, password input is aborted if the user is idle for too long. The default timeout is infinite.


Turns on lots of progress reporting. Higher numbers give more verbose output. If −v is additionally specified on the lilo command line, the level is increased accordingly. The maximum verbosity level is 5.

Additionally, the kernel configuration parameters append, ramdisk, read-only, read-write, root and vga can be set in the global options section. They are used as defaults if they aren’t specified in the configuration sections of the respective kernel images.


A per-image section starts with either a line


(to indicate a file or device containing the boot image of a Linux kernel), or a line


to indicate an arbitrary system to boot.

In the former case, if an image line specifies booting from a device, then one has to indicate the range of sectors to be mapped using

In the latter case (booting another system) there are the three options

This specifies the chain loader that should be used. By default /boot/chain.b is used. The chain loader must be specified if booting from a device other than the first hard or floppy disk.


This specifies the device that contains the partition table. The boot loader will not pass partition information to the booted operating system if this variable is omitted. (Some operating systems have other means to determine from which partition they have been booted. E.g., MS-DOS usually stores the geometry of the boot disk or partition in its boot sector.) Note that /sbin/lilo must be re-run if a partition table mapped referenced with ’table’ is modified.


Do not access the boot sector at map creation time. This disables some sanity checks, including a partition table check. If the boot sector is on a fixed-format floppy disk device, using UNSAFE avoids the need to put a readable disk into the drive when running the map installer. ’unsafe’ and ’table’ are mutually incompatible.

In both cases the following options apply.

The boot loader uses the main file name (without its path) of each image specification to identify that image. A different name can be used by setting the variable ’label’.


A second name for the same entry can be used by specifying an alias.


(See above.)


Omit the image if it is not available at map creation time. This is useful to specify test kernels that are not always present.


Protect the image by a password.


A password is only required to boot the image if parameters are specified on the command line (e.g. single).


If the booted image is a Linux kernel, then one may pass command line parameters to this kernel.

Appends the options specified to the parameter line passed to the kernel. This is typically used to specify parameters of hardware that can’t be entirely auto-detected or for which probing may be dangerous. Example:

append = "hd=64,32,202"


Like ’append’, but removes all other options (e.g. setting of the root device). Because vital options can be removed unintentionally with ’literal’, this option cannot be set in the global options section.


This specifies the size of the optional RAM disk. A value of zero indicates that no RAM disk should be created. If this variable is omitted, the RAM disk size configured into the boot image is used.


This specifies that the root file system should be mounted read-only. Typically, the system startup procedure re-mounts the root file system read-write later (e.g. after fsck’ing it).


This specifies that the root file system should be mounted read-write.


This specifies the device that should be mounted as root. If the special name current is used, the root device is set to the device on which the root file system is currently mounted. If the root has been changed with -r , the respective device is used. If the variable ’root’ is omitted, the root device setting contained in the kernel image is used. (And that is set at compile time using the ROOT_DEV variable in the kernel Makefile, and can later be changed with the rdev(8) program.)


This specifies the VGA text mode that should be selected when booting. The following values are recognized (case is ignored):

normal: select normal 80x25 text mode.

extended (or ext): select 80x50 text mode.

ask: stop and ask for user input (at boot time).

<number>: use the corresponding text mode. A list of available modes can be obtained by booting with vga=ask and pressing [Enter].

If this variable is omitted, the VGA mode setting contained in the kernel image is used. (And that is set at compile time using the SVGA_MODE variable in the kernel Makefile, and can later be changed with the rdev(8) program.)


lilo(8), rdev(8).
The lilo distribution comes with very extensive documentation of which the above is an extract.