Making a Dedicated Grub
Copyright (C) 2006 by Steve Litt,
rights reserved. Material
provided as-is, use at your own risk.
This document contains a series of exercises accessing, and in some
cases overwriting, your boot loader. There's a significant possibility
of overwriting your existing boot loader, which can lead to lost time
and even lost data. There may be other risks.
You use this document at your own risk. I am not responsible
for any damage or injury caused by your use of this document, or caused
by errors and/or omissions in this document. If that's not acceptable
you, you may not use this document. By using this document you are
accepting this disclaimer.
I'm not a Windows authority. I stopped buying commercial software in
1999, therefore never upgrading Windows past Win98 version 1. My
knowledge of Win2K and WinXP is that of an occasional user (at somebody
else's office). Therefore, I cannot tell you how to dual boot
It's absolutely essential you undertand the contents of Grub From the Ground Up before attempting anything
on this page!
If you've ever had four or more Linux distros on one box, you already
know the answer. Install a new distro, and you lose the ability to boot
the others. Oh sure, some distros are nice enough to try to detect the
others, but often label them wrong. Some distros don't even try, but
assume they're the only distro on the disk. Some distros overwrite
everything with LILO.
When installing, removing and tweaking multiple distros on a
single box, what you really need is a single menu of all boots.
Ideally, you don't want that menu associated with a distro, because it
it were, it would be overwritten every time you remove or reinstall
This document walks you through creating a 1 MB hard disk partition
containing the grub boot code and the grub menu for all your various
boots. By keeping this one and only one menu up to date, you avoid the
confusion of constantly having to re-import all other boots every time
you install something new. Because the partition is only a single
megabyte, you avoid the temptation to cannibalize it for something else.
Once your grub partition is in place, adding a distro is as simple as
installing that distro, then mounting the grub partition, and adding
the new distro's grub boot information (menu.lst) to the boot distro's menu.lst, and then resetting the hard disk MBR to point to the grub partition.
Creating Your Grub Partition
Unless you have very strange hardware with special booting needs, you
can fit all Grub code into a 1MB partition. Create the partition with fdisk. The fdisk program is able to make tiny partitions not on cylinder boundaries. Other programs such as cfdisk
round to the nearest cylinder boundary, thereby making this partition
much bigger than it needs to be. For the same reason, use fdisk
to create the partition after this one, to make sure that no space is
left in the middle. From then on, assuming partitions are big, other
partitioning programs are fine, because a few megabytes on one side or
the other of a 2GB partition aren't significant.
If you're working with a very old bios with the ancient 1024 cylinder
limitation, it should be very near the front of the disk (make it
/dev/hda1). Remember, it's only a megabyte in size, so it's not going
to "push out" any other partitions with this limitation (typically the
/boot partition). As a practical matter, modern bios implementations
don't have this limitation, so on modern machines you can put the grub
Try to make sure to remember the device number (/dev/hda1)
or whatever) housing the grub partition. However, if worst comes to
worst, you can quickly see which partition using this command:
fdisk -lu /dev/hda
The preceding command prints out the number of sectors used by each
partition. The Grub partition will be the smallest, because no modern
operating system can be housed in a 1MB partition.
Once you've used fdisk to create the partition, format it with the mkfs.ext2 command. There's no use making this an ext3 partition, because it's small enough to fsck anyway.
Setting Up Your Grub Partition
This is simply a matter of copying files. At the very least, you must have these three files:
You can copy stage1 and stage2 from the /boot/grub
directory of the booted OS, or any partition. However, if you have any
unusual hardware or journaling file systems besides ext3, you'll need
some of the "stage1_5" files. In such a case, ALL the stage files must
be copied from the same source. On your currently booted distro,
perform the following command:
Here are some of the files that command shows on my Mandriva 2006 system:
I could copy ALL those files to the grub partition, or just stage1 and stage2.
Here's how I'd do it:
Note that on my system, a du command reveals that all those files consume only 376KB, so there's plenty of room.
mount /dev/hda1 /mnt/test
mkdir -p /mnt/test/boot/grub
cp -p /lib/grub/i386-mandriva/* /mnt/test/boot/grub
The only thing left to do is create /mnt/test/boot/grub/menu.lst.
Making Your menu.lst
If possible, find a partition whose menu.lst contains choices for booting several different partitions. If the partition having such a menu.lst were /dev/hda7 and your Grub partition were /dev/hda1, and you mounted them as /mnt/hda1 and /mnt/hda7, you'd perform the following command:
cp /mnt/hda7/boot/grub/menu.lst /mnt/hda1/boot/grub
Now that you have a starter for menu.lst, edit the file and pull in the info from menu.lst
files from other partitions, straight into your editor. In each case,
delete out the new global information and keep only the info for each
new boot. Be careful that you don't get two different choices for
essentially the same boot.
Occasionally, on LILO-only distributions, you might find no menu.lst file. In that case, import that distro's /etc/lilo.conf and translate LILO menu info to Grub menu info. It's not difficult if you do it slowly.
As you edit the file, make different versions so that if it doesn't work you can try a simpler version.
Making it Happen at Boot Time
You've made your menu.lst
on your Grub partition, complete with boot info from every distro on
the system. The trouble is, that menu file won't be consulted at boot
time. To get the boot to consult it, you need to tell the hard disk's
MBR to consult your Grub partition. Assuming your Grub partition is /dev/hda1, here's how you do it:
In the preceding command sequence, the first runs the grub executable. The second sets the root to (hd0,0), which is grub-speak for /dev/hda1. The third command tells grub to install code on the MBR that looks to /dev/hda1 for boot code. The fourth command terminates the grub
command, and the fifth reboots the computer. When the computer reboots,
if all went well you should see the menu you set up on your grub
partition. If not, troubleshoot. If need be, bust back into the machine
using the Grub techniques on the Grub From the Ground Up page, using either a Grub floppy or a Knoppix CD.
grub> root (hd0,0)
grub> setup (hd0)
Adding a New Distro
This is where you start to see the real benefit of the dedicated Grub
partition. In the bad old days, installing one more distro on your hard
disk would necessitate a long and difficult search for other boots,
culminating in voluminous troubleshooting. Now you simply edit your
Grub partition's menu.lst and add the boots (not the globals) from the latest distro addition. Booted into the latest distro, signed in as root, it would go something like this:
- Mount /dev/hda1 /mnt/test
- cd /mnt/test/boot/grub
- cp -p menu.lst menu.lst.bup
- vim menu.lst
- Within vim:
- G to get to the bottom
- o <Enter><Enter><Enter><Enter> (in order to open a space)
- :r /boot/grub/menu.lst
- NOTE: If the new version had /etc/lilo.conf and no
/boot/grub/menu.lst, you might need to read in lilo.conf and then
translate. It's not particularly difficult.
- Delete all global info brought in by the new menu.lst, and also any boots you don't need.
- Run Grub, and within Grub do this:
- grub> root (hd0,0)
- setup (hd0)
- Reboot the computer, and your list should include all old boots as well as those brought in by the new boots.
The Case for Doing this On Every Hard Disk
A tiny dedicated Grub partition makes it easy to include a dedicated
Knoppix partition, along with anything else you might need on the hard
I find life much easier with a Knoppix partition on every hard disk I
own. On dedicated data drives, it allows me to grab my data if my
system drive should become defunct. It allows easy transfer of data
between an old data disk and its replacement, either with the old disk
still in the production computer and the new disk in a spare computer,
or the new disk in the production computer and the old disk in the
spare computer (in other words, you forgot to do it before shutting
down the production computer with the old disk -- it happens).
You never know when somebody, some time, will dual or tri-boot the
system. Or install six different OS's on it. Having a dedicated Grub
partition makes such events much easier to handle.