Lilo mini-Howto

Lilo mini-Howto
Cameron Spitzer ([email protected]), Alessandro Rubini
([email protected]).
v2.02, 16 August 1998

LILO is the most used Linux Loader for the x86 flavour of Linux; I'll
call it Lilo rather than LILO here because I don't appreciate upper
case. This file describes some typical Lilo installations. It's
intended as a supplement to the Lilo User's Guide. I think examples
are informative even if your setup isn't much like mine. I hope this
saves you trouble. Since Lilo's own documentation is very good, who's
interested in the details is referred to /usr/doc/lilo*
______________________________________________________________________

Table of Contents

1. Introduction

2. Background Information and Standard Installation

2.1 Where Should I Install Lilo?
2.2 How Should I Configure my IDE Hard Drives?
2.3 How Can I Interact at Boot Time?
2.4 How Can I Uninstall Lilo?

3. The Simple Configuration

3.1 How to Deal with Big Kernels
3.2 Other Sources of Information

4. Installing

5. Using Lilo When the BIOS Can't See the Root Partition

6. Accessing Huge Disks When the BIOS Can't

7. Booting from a Rescue Floppy

______________________________________________________________________

1. Introduction

Although the documentation found in Lilo's sources (the one installed
in /usr/doc/lilo-version) is very comprehensive, most Linux users
experience some trouble in building their own /etc/lilo.conf file.
This document is meant to support them by giving the minimal
information and by showing five sample installations:

The first example is the classical ``Linux and other''
installation.

The next one shows how to install Lilo on a hard drive connected as
/dev/hdc that will boot as /dev/hda. This is usually needed when
you install a new Linux drive from your own running system. This
also tells how to boot from SCSI disks when your BIOS is modern
enough.

The third example shows how to boot a Linux system whose root
partition can't be accessed by the BIOS.

The next sample file is used to access huge disks, that neither the
BIOS nor DOS can access easily (this one is somehow outdated).
The last example shows how to restore a damaged disk, if the damage
resulted from installing another operating system).

The last three examples are by Cameron, [email protected], who
wrote the original document. Alessandro (tt/[email protected]/, the
current maintainer doesn't run anything but Linux, so he can't check
nor update them by himself. Needless to say, any feedback is welcome.

2. Background Information and Standard Installation

When Lilo boots the system, it uses BIOS calls to load the Linux
kernel off the disk (IDE drive, floppy or whatever). Therefore, the
kernel must live in some place that can be accessed by the bios.

At boot time, Lilo is not able to read filesystem data, and any
pathname you put in /etc/lilo.conf is resolved at installation time
(when you invoke /sbin/lilo). Installation time is when the program
builds the tables that list which sectors are used by the files used
to load the operating system. As a consequence, all of these files
must live in a partition that can be accessed by the BIOS (the files
are usually located in the /boot directory, this means that only the
root partition of your Linux system needs to be accessed via the
BIOS).

Another consequence of being BIOS-based is that you must reinstall the
loader (i.e., you must reinvoke /sbin/lilo) any time you modify the
Lilo setup. Whenever you recompile your kernel and overwrite your old
image you must reinstall Lilo.

2.1. Where Should I Install Lilo?

The boot= directive in /etc/lilo.conf tells Lilo where it should place
its primary boot loader. In general, you can either specify the master
boot record (/dev/hda) or the root partition of your Linux
installation (is usually is /dev/hda1 or /dev/hda2).

If you have another operating system installed in your hard drive,
you'd better install Lilo to the root partition instead of the MBR. In
this case, you must mark the partition as ``bootable'' using the ``a''
command of fdisk or the ``b'' command of cfdisk. If you don't
overwrite the master boot sector you'll find it easier to uninstall
Linux and Lilo if needed.

2.2. How Should I Configure my IDE Hard Drives?

I personally don't use LBA or LARGE settings in the BIOS (but I only
run Linux); they are horrible kludges forced on by design deficiencies
in the PC world. This requires that the kernel lives in the first 1024
cylinders, but this is not a problem as long as you partition your
hard drives and keep root small (as you should do anyways).

If your hard disk already carries another operating system, you won't
be able to modify the BIOS settings, or the old system won't work any
more. All recent Lilo distribution are able to deal with LBA and LARGE
disk settings.

Note that the "linear" keyword in /etc/lilo.conf can help in dealing
with geometry problems. The keyword instructs Lilo to use linear
sector addresses instead of sector/head/cylinder tuples. Conversion
to 3D addresses is delayed to run-time, therefore making the setup
more immune to geometry problems.

If you have more than one hard disk and some of them are only used by
Linux and are not involved in the boot process, you can tell your BIOS
that they are not installed. Your system will boot more quickly and
Linux will autodetect all the disks in no time. I often switch disks
in my computers, but I never touch the BIOS configuration.

2.3. How Can I Interact at Boot Time?

When you see the Lilo prompt, you can hit the <Tab> key to show the
list of possible choices. If Lilo is not configured to be interactive,
press and hold the <Alt> or <Shift> key before the ``LILO'' message
appears.

If you choose to boot a Linux kernel, you can add command-line
arguments after the name of the system you choose. The kernel accepts
many command-line arguments. All the arguments are listed in the
``BootPrompt-HOWTO'' by Paul Gortmaker, and I won't replicate it here.
A few command line arguments, however, are particularly important and
worth describing here:

root=: you can tell the Linux kernel to mount as root a different
partition than the one appearing in lilo.conf. For example, my
system has a tiny partition hosting a minimal Linux installation,
and I've been able to boot the system after destroying my root
partition by mistake.

init=: verson 1.3.43 and newer of the Linux kernel can execute
another command instead of /sbin/init, as specified on the command
line. If you experience bad problems during the boot process, you
can access the bare system by specifying init=/bin/sh (when you are
at the shell prompt you most likely will need to mount your disks:
try ``mount -w -n -o remount /; mount -a'', and remember to
``umount -a'' before turning off the computer).

A number: by specifying a number on the kernel command line, you
instruct init to enter a specific run-level (the default is usually
3 or 2, according to the distribution you chose). Refer to the
init documentation, to /etc/inittab and to /etc/rc*.d to probe
further.

2.4. How Can I Uninstall Lilo?

When Lilo overwrites a boot sector, it saves a backup copy in
/boot/boot.xxyy, where xxyy are the major and minor numbers of the
device, in hex. You can see the major and minor numbers of your disk
or partition by running ``ls -l /dev/device''. For example, the first
sector of /dev/hda (major 3, minor 0) will be saved in
/boot/boot.0300, installing Lilo on /dev/fd0 creates /boot/boot.0200
and installing on /dev/sdb3 (major 8, minor 19) creates
/boot/boot.0813. Note that Lilo won't create the file if there is
already one so you don't need to care about the backup copy whenever
you reinstall Lilo (for example, after recompiling your kernel). The
backup copies found in /boot/ are always the snapshot of the situation
before installing any Lilo.

If you ever need to uninstall Lilo (for example, in the unfortunate
case you need to uninstall Linux), you just need to restore the
original boot sector. If Lilo is installed in /dev/hda, just do ``dd
if=/boot/boot.0300 of=/dev/hda bs=446 count=1'' (I personally just do
``cat /boot/boot.0300 > /dev/hda'', but this is not safe, as this will
restore the original partition table as well, which you might have
modified in the meanwhile). This command is much easier to run than
trying ``fdisk /mbr'' from a DOS shell: it allows you to cleanly
remove Linux from a disk without ever booting anything but Linux.
After removing Lilo remember to run Linux' fdisk to destroy any Linux
partition (DOS' fdisk is unable to remove non-dos partitions).

If you installed Lilo on your root partition (e.g., /dev/hda2),
nothing special needs to be done to uninstall Lilo. Just run Linux'
fdisk to remove Linux partitions from the partition table. You must
also mark the DOS partition as bootable.

3. The Simple Configuration

Most Lilo installations use a configuration file like the following
one:

boot = /dev/hda # or your root partition
delay = 10 # delay, in tenth of a second (so you can interact)
vga = 0 # optional. Use "vga=1" to get 80x50
#linear # try "linear" in case of geometry problems.

image = /boot/vmlinux # your zImage file
root = /dev/hda1 # your root partition
label = Linux # or any fancy name
read-only # mount root read-only

other = /dev/hda4 # your dos partition, if any
table = /dev/hda # the current partition table
label = dos # or any non-fancy name

You can have multiple ``image'' and ``other'' sections if you want.
It's not uncommon to have several kernel images configured in your
lilo.conf, at least if you keep up to date with kernel development.

3.1. How to Deal with Big Kernels

If you compile a ``zImage'' kernel and it is too big to fit in half a
megabyte (this is commong with new 2.1 kernels), you should build a
``big zImage'' instead: ``make bzImage''. To boot a big kernel image
nothing special is needed, but you need version 18 or newer of Lilo.
If your installation is older, you should upgrade your Lilo package.

3.2. Other Sources of Information

In addition to the Lilo docs, there are a number of mini-howto's that
can be useful for your needs. All of them are called
``Linux+foobarOS'', for some foobarOS, they deal with coexistence of
Linux and other operationg system(s). Also, ``Multiboot-with-LILO''
describes how the various Windows flavours can be made to coexist with
Linux.

4. Installing hdc to Boot as hda and Using bios=

Lilo allows to map the kernel image from one disk and instruct the
BIOS to retrieve it from another disk. For example, it's common for me
to install Linux on a disk I connect to hdc (master disk of secondary
controller) and boot it as a standalong system on the primary IDE
controller of another computer. I copied the installation floppy to a
tiny partition, so I can run chroot in a virtual console to install
hdc while I use the system to do something else.

The lilo.conf file I use to install Lilo looks like:

# This file must be used from a system running off /dev/hdc
boot = /dev/hdc # overwrite MBR of hdc
disk = /dev/hdc # tell how hdc will look like:
bios = 0x80 # the bios will see it as first drive
delay = 0
vga = 0

image = /boot/vmlinux # this is on /dev/hdc1
root = /dev/hda1 # but at boot it will be hda1
label = Linux
read-only

This configuration file must be read by a Lilo running off /dev/hdc1.
The Lilo maps that get written the boot sector (/dev/hdc) must refer
to the files in /boot (currently installed as hdc); such files will be
accessed under hda when this disk will be booted as a standalone
system.

I call this configuration file /mnt/etc/lilo.conf.hdc (/mnt is where
hdc is mounted during the installation. I install Lilo by invoking
``cd /mnt; chroot . sbin/lilo -C /etc/lilo.conf.hdc''. Refer to the
manual page for chroot if this looks magic.

The ``bios='' directive in lilo.conf is used to tell Lilo what the
BIOS thinks of your devices. BIOS calls identify floppy disks and hard
drives with a number: 0x00 and 0x01 select the floppy drives, 0x80 and
the following numbers select hard disks (old BIOSes can only access
two disks). The meaning of ``bios = 0x80 in the previous sample file
is therefore ``use 0x80 in your BIOS calls for /dev/hdc''.

This Lilo directive can be handy in other situations, for example when
your BIOS is able to boot from SCSI disks instead of IDE ones. When
both IDE and SCSI devices are there, Lilo can't tell whether 0x80 will
refer to one or the other because the user is able to choose it in the
BIOS configuration menus, and the BIOS can't be accessed while Linux
is running.

By default, Lilo assumes that IDE drives are mapped first by the BIOS,
but this can be overridden by using instructions like these in
/etc/lilo.conf:

disk = /dev/sda
bios = 0x80

5. Using Lilo When the BIOS Can't See the Root Partition

I have two IDE drives, and a SCSI drive. The SCSI drive can't be seen
from BIOS. The Linux Loader, Lilo, uses BIOS calls and can only see
drives that BIOS can see. My stupid AMI BIOS will only boot from "A:"
or "C:" My root file system is on a partition on the SCSI drive.

The solution consists in storing the kernel, map file, and chain
loader in a Linux partition on the first IDE. Notice that it is not
necessary to keep your kernel on your root partition.

The second partition on my first IDE (/dev/hda2, the Linux partition
used to boot the system) is mounted on /u2. Here is the
/etc/lilo.conf file I used.

# Install Lilo on the Master Boot Record
# on the first IDE.
#
boot = /dev/hda
# /sbin/lilo (the installer) copies the Lilo boot record
# from the following file to the MBR location.
install = /u2/etc/lilo/boot.b
#
# I wrote a verbose boot menu. Lilo finds it here.
message = /u2/etc/lilo/message
# The installer will build the following file. It tells
# the boot-loader where the blocks of the kernels are.
map = /u2/etc/lilo/map
compact
prompt
# Wait 10 seconds, then boot the 1.2.1 kernel by default.
timeout = 100
# The kernel is stored where BIOS can see it by doing this:
# cp -p /usr/src/linux/arch/i386/boot/zImage /u2/z1.2.1
image = /u2/z1.2.1
label = 1.2.1
# Lilo tells the kernel to mount the first SCSI partition
# as root. BIOS does not have to be able to see it.
root = /dev/sda1
# This partition will be checked and remounted by /etc/rc.d/rc.S
read-only
# I kept an old Slackware kernel lying around in case I built a
# kernel that doesn't work. I actually needed this once.
image = /u2/z1.0.9
label = 1.0.9
root = /dev/sda1
read-only
# My DR-DOS 6 partition.
other = /dev/hda1
loader=/u2/etc/lilo/chain.b
label = dos
alias = m

6. Accessing Huge Disks When the BIOS Can't

The system in my office has a 1GB IDE drive. The BIOS can only see
the first 504 MB of the IDE. (Where MB means 2**10 bytes, not 10**6
bytes.) So I have MS-DOS on a 350 MB partition /dev/hda1 and my Linux
root on a 120 MB partition /dev/hda2.

MS-DOS was unable to install itself correctly when the drive was
fresh. Novell DOS 7 had the same problem. Luckily for me, "Options
by IBM" forgot to put the "OnTrack" diskette in the box with the
drive. The drive was supposed to come with a product called "OnTrack
Disk Manager." If you only have MSDOS, I guess you have to use it.

So I made a partition table with Linux' fdisk. MSDOS-6.2 refused to
install itself in /dev/hda1. It said something like ``this release of
MS-DOS is for new installations. Your computer already has MS-DOS so
you need to get an upgrade release from your dealer.'' Actually, the
disk was brand new.

What a crock! So I ran Linux' fdisk again and deleted partition 1
from the table. This satisfied MS-DOS 6.2 which proceeded to create
the exact same partition 1 I had just deleted and installed itself.
MS-DOS 6.2 wrote its Master Boot Record on the drive, but it couldn't
boot.

Luckily I had a Slackware kernel on floppy (made by the Slackware
installation program "setup"), so I booted Linux and wrote Lilo over
MS-DOS' broken MBR. This works. Here is the /etc/lilo.conf file I
used:

boot = /dev/hda
map = /lilo-map
delay = 100
ramdisk = 0 # Turns off ramdisk in Slackware kernel
timeout = 100
prompt
disk = /dev/hda # BIOS only sees first 500 MB.
bios = 0x80 # specifies the first IDE.
sectors = 63 # get the numbers from your drive's docs.
heads = 16
cylinders = 2100
image = /vmlinuz
append = "hd=2100,16,63"
root = /dev/hda2
label = linux
read-only
vga = extended
other = /dev/hda1
label = msdos
table = /dev/hda
loader = /boot/chain.b

After I installed these systems, I verified that the partition
containing the zImage, boot.b, map, chain.b, and message files can use
an msdos file system, as long as it is not "stackered" or
"doublespaced." So I could have made the DOS partition on /dev/hda1
500 MB.

I have also learned that "OnTrack" would have written a partition
table starting a few dozen bytes into the drive, instead of at the
beginning, and it is possible to hack the Linux IDE driver to work
around this problem. But installing would have been impossible with
the precompiled Slackware kernel. Eventually, IBM sent me an
"OnTrack" diskette. I called OnTrack's technical support. They told
me Linux is broken because Linux doesn't use BIOS. I gave their
diskette away.

7. Booting from a Rescue Floppy

Next, I installed Windows-95 on my office system. It blew away my
nice Lilo MBR, but it left my Linux partitions alone. Kernels take a
long time to load from floppy, so I made a floppy with a working Lilo
setup on it, which could boot my kernel from the IDE.

I made the lilo floppy like so:

fdformat /dev/fd0H1440 # lay tracks on virgin diskette
mkfs -t minix /dev/fd0 1440 # make file system of type minix
mount /dev/fd0 /mnt # mount in the standard tmp mount point
cp -p /boot/chain.b /mnt # copy the chain loader over
lilo -C /etc/lilo.flop # install Lilo and the map on the diskette.
umount /mnt

Notice that the diskette must be mounted when you run the installer so
that Lilo can write its map file properly.

This file is /etc/lilo.flop. It's almost the same as the last one:

# Makes a floppy that can boot kernels from HD.
boot = /dev/fd0
map = /mnt/lilo-map
delay = 100
ramdisk = 0
timeout = 100
prompt
disk = /dev/hda # 1 GB IDE, BIOS only sees first 500 MB.
bios=0x80
sectors = 63
heads = 16
cylinders = 2100
image = /vmlinuz
append = "hd=2100,16,63"
root = /dev/hda2
label = linux
read-only
vga = extended
other = /dev/hda1
label = msdos
table = /dev/hda
loader = /mnt/chain.b

Finally, I needed MS-DOS 6.2 on my office system, but I didn't want to
touch the first drive. I added a SCSI controller and drive, made an
msdos file system on it with Linux' mkdosfs, and Windows-95 sees it as
"D:". But of course MSDOS will not boot off of D:. This is not a
problem when you have Lilo. I added the following to the lilo.conf in
Example 2.

other = /dev/sda1
label = d6.2
table = /dev/sda
loader = /boot/any_d.b

With this modification MSDOS-6.2 runs, and it thinks it is on C: and
Windows-95 is on D:.