The Linux+FreeBSD mini-HOWTO
Niels Kristian Bech Jensen, nkbj@image.dk
v1.7, 18 June 1998
This document describes how to use Linux and FreeBSD on the same sys
tem. It introduces FreeBSD and discusses how the two operating systems
can cooperate, e.g. by sharing swap space. You should probably have
some experience with Linux or FreeBSD and hard drive partitioning
(fdisk) before you read this document. The tips herein are tested
using FreeBSD 2.2.2, but they should be valid for newer versions as
well. Do not hesitate to mail me if you have comments, questions or
suggestions about this document. I would also like to hear from people
who have experience using Linux together with NetBSD or OpenBSD.
______________________________________________________________________
Table of Contents
1. What is FreeBSD?
2. The FreeBSD way of labelling hard drives
2.1 FreeBSD ``slices'' and ``partitions''
2.2 Drive and partition labelling in Linux and FreeBSD
3. Sharing swap space between Linux and FreeBSD
3.1 Installing and preparing Linux
3.2 Installing FreeBSD
3.3 Setting up the FreeBSD swap partition in Linux
4. Booting FreeBSD using LILO
5. Mounting file systems
5.1 Mounting UFS file systems under Linux
5.2 Mounting ext2fs file systems under FreeBSD
6. Running foreign binaries
6.1 Running FreeBSD binaries under Linux
6.2 Running Linux binaries under FreeBSD
7. References and other documents of interest
8. Acknowledgments and Copyright
8.1 Disclaimer
8.2 Copyright
______________________________________________________________________
1. What is FreeBSD?
FreeBSD is a free Unix-like operating system much like Linux. The main
difference is that, while the Linux kernel has been written from
scratch, FreeBSD is based on the freely redistributable parts of
4.4BSD (Berkeley Software Distribution) known as 4.4BSD-lite. This
fact might lead some people to suggest that FreeBSD is closer to being
``real'' UNIX(TM) than Linux. FreeBSD runs only on the Intel PC
platform (i386 and higher); ports to the DEC Alpha and Sun Sparc
platforms are being worked on at the moment. Hardware requirements
for FreeBSD are much like those for Linux.
The development of FreeBSD is managed in a different way than the
Linux development. A core team of developers serve as arbitrators and
provide leadership for the project. Big changes are discussed in
advance on the mailing lists. The FreeBSD project has two development
trees (just like Linux): ``-CURRENT'' and ``-STABLE''. The
``-CURRENT'' development tree is where the development of new features
happens. Development to the ``-STABLE'' tree are restricted to bug
fixes and some thoroughly tested new features.
FreeBSD can be used and (re-)distributed freely just as Linux. Most
parts of the system are released under the BSD copyright; the rest is
under the GNU GPL or the GNU LGPL.
You can find more information about FreeBSD (and download the whole
system) at The FreeBSD Project Homepage . The
newest ``-STABLE'' releases and snapshots of the ``-CURRENT''
development code are sold on CDROMs by Walnut Creek CDROM
(their web- and ftp-servers are running
FreeBSD.)
2. The FreeBSD way of labelling hard drives
Linux and FreeBSD label hard drives and partitions after two
differents schemes. This section explains the main differences between
the two schemes. In fact the FreeBSD labelling scheme is an adaption
of the traditional BSD labelling style ported to live within the PC's
fdisk partitions. Thus it is very similar to other BSD-based Unix
systems such as NetBSD, OpenBSD, Ultrix, Digital Unix, SunOS, and
Solaris.
2.1. FreeBSD ``slices'' and ``partitions''
FreeBSD needs one of the four entries in the partition table on your
PC's hard drive. This primary partition is called a ``slice'' in
FreeBSD terminology. It then uses the disklabel program to make up to
eight partitions in this primary partition. These logical partitions
are called ``partitions'' in FreeBSD terminology. This concept is
similar to the way Linux (and DOS) handles logical partitions in an
extended partition. You can't install FreeBSD in an extended partition
made by Linux (or DOS). Note that the Linux fdisk program doesn't
display the BSD partitions in a FreeBSD slice from the main menu, but
it can display BSD disklabel information if you give the command `b'.
The output is something like this (/dev/hda4 is the FreeBSD slice):
bash# fdisk /dev/hda
Command (m for help): p
Disk /dev/hda: 64 heads, 63 sectors, 621 cylinders
Units = cylinders of 4032 * 512 bytes
Device Boot Begin Start End Blocks Id System
/dev/hda1 * 1 1 27 54400+ 83 Linux native
/dev/hda2 28 28 55 56448 83 Linux native
/dev/hda3 56 56 403 701568 83 Linux native
/dev/hda4 404 404 621 439488 a5 BSD/386
Command (m for help): b
Reading disklabel of /dev/hda4 at sector 1624897.
BSD disklabel command (m for help): p
8 partitions:
# size offset fstype [fsize bsize cpg]
a: 64512 1624896 4.2BSD 0 0 0 # (Cyl. 404 - 419)
b: 104832 1689408 swap # (Cyl. 420 - 445)
c: 878976 1624896 unused 0 0 # (Cyl. 404 - 621)
e: 64512 1794240 4.2BSD 0 0 0 # (Cyl. 446 - 461)
f: 645120 1858752 4.2BSD 0 0 0 # (Cyl. 462 - 621)
BSD disklabel command (m for help): q
bash#
The letters `a'...`f' in the first column are the same labels as shown
below in the example for a FreeBSD slice. There are three special
partitions in BSD parlace. The letter `a' designates the root
partition, `b' designates the swap partition, while `c' designates the
whole slice. See the FreeBSD documentation for more information on the
``standard'' way of assigning these letters to different partition
types.
2.2. Drive and partition labelling in Linux and FreeBSD
The hard drives are labelled in the following way in Linux and
FreeBSD:
Linux FreeBSD
First IDE drive /dev/hda /dev/wd0
Second IDE drive /dev/hdb /dev/wd1
First SCSI drive /dev/sda /dev/sd0
Second SCSI drive /dev/sdb /dev/sd1
The partitions (FreeBSD slices) on an IDE drive are labelled in the
following way (/dev/hda is used as an example):
Linux FreeBSD
First primary partition /dev/hda1 /dev/wd0s1
Second primary partition /dev/hda2 /dev/wd0s2
Third primary partition /dev/hda3 /dev/wd0s3
Fourth primary partition /dev/hda4 /dev/wd0s4
The partitions in my FreeBSD slice is labelled in the following way.
It is the labelling you get by default. It is possible to change the
labelling if you do a custom installation of FreeBSD (/dev/hda4 is the
FreeBSD slice in the example):
Linux label FreeBSD label FreeBSD mount point
/dev/hda5 /dev/wd0s4a /
/dev/hda6 /dev/wd0s4b swap
/dev/hda7 /dev/wd0s4e /var
/dev/hda8 /dev/wd0s4f /usr
If you run dmesg in Linux you will see this as (The linux kernel must
be build with UFS filesystem support for this to work. See section
``Installing and preparing Linux''):
Partition check:
hda: hda1 hda2 hda3 hda4 < hda5 hda6 hda7 hda8 >
If you have installed FreeBSD in the /dev/sd1s3 slice (/dev/sdb3 in
Linux parlace), and /dev/sdb2 is a Linux extended partition containing
two logical partitions (/dev/sdb5 and /dev/sdb6), the previous example
would look like this:
Linux label FreeBSD label FreeBSD mount point
/dev/sdb7 /dev/sd1s3a /
/dev/sdb8 /dev/sd1s3b swap
/dev/sdb9 /dev/sd1s3e /var
/dev/sdb10 /dev/sd1s3f /usr
This will be shown as
Partition check:
sdb: sdb1 sdb2 < sdb5 sdb6 > sdb3 < sdb7 sdb8 sdb9 sdb10 >
in the output from dmesg.
If you have a Linux extended partition after your FreeBSD slice you're
in for trouble, because most Linux kernels installation floppies are
build without UFS support, they will not recognise the FreeBSD
partitions inside the slice. What should have have been seen as
(/dev/hda3 is the FreeBSD slice and /dev/hda4 is the Linux extended
partition)
Partition check:
hda: hda1 hda2 hda3 < hda5 hda6 hda7 hda8 > hda4 < hda9 hda10 >
is seen as:
Partition check:
hda: hda1 hda2 hda3 hda4 < hda5 hda6 >
This can give you the wrong device assignment and cause the loss of
data. My advice is to always put your FreeBSD slice after any Linux
extended partitions, and do not change any logical partitions in your
Linux extended partitions after installing FreeBSD!
3. Sharing swap space between Linux and FreeBSD
This section describes how I got Linux and FreeBSD to share a swap
partition. There may be other ways to get the same result. You can
install FreeBSD before Linux if you want to, just pay attention to the
order of the partitions in the FreeBSD slice.
3.1. Installing and preparing Linux
The first step is to install Linux as normal. You have to leave space
for the FreeBSD slice at your hard drive. You don't have to make a
Linux swap partition, but if you want one, put it in the space you
want to allocate for FreeBSD. That way you can delete the Linux swap
partition later and use the space for FreeBSD.
When you have installed Linux you have to build a new kernel. Read The
Linux Kernel HOWTO if this is new to you. You have to include both UFS
filesystem support (read only) and BSD disklabel (FreeBSD partition
tables) support:
UFS filesystem support (read only) (CONFIG_UFS_FS) [N/y/m/?] y
BSD disklabel (FreeBSD partition tables) support (CONFIG_BSD_DISKLABEL) [N/y/?]
(NEW) y
Install the new kernel and reboot. Remove any line including the word
swap from your /etc/fstab file if you have made a Linux swap
partition. Make sure you have a working Linux boot floppy with the
new kernel. Now you are ready to install FreeBSD.
3.2. Installing FreeBSD
Install FreeBSD as described in the FreeBSD documentation. Remove the
Linux swap partition if you have made one (you can use the FreeBSD
fdisk program.) Pay attention to the order of the partitions in the
FreeBSD slice. If you use the default labelling the second partition
will be the swap partition. Complete the installation of FreeBSD and
reboot into Linux using the new Linux boot floppy.
3.3. Setting up the FreeBSD swap partition in Linux
Run dmesg when you have booted into Linux. In the output you should
see something like this:
Partition check:
hda: hda1 hda2 hda3 hda4 < hda5 hda6 hda7 hda8 >
This means that /dev/hda4 is your FreeBSD slice, while /dev/hda5,
/dev/hda6, /dev/hda7 and /dev/hda8 are the FreeBSD partitions. If your
swap partition is the second partition in the slice, it will be
/dev/hda6.
You have to put the following line into your Linux /etc/fstab file to
enable the swap partition:
/dev/hda6 none swap sw 0 0
While FreeBSD can use any type of partition as swap space, Linux needs
a special signature in the swap partition. This signature is made by
mkswap. FreeBSD ruins this signature when it uses the shared swap
partition, so you will have to run mkswap each time you boot into
Linux. To do this automagically you have to find the script that runs
swapon at boot time. In Red Hat Linux it is /etc/rc.d/rc.sysinit. Put
the following line into that file just before swapon -a:
awk -- '/swap/ && ($1 !~ /#/) { system("mkswap "$1"") }' /etc/fstab
This will run mkswap on any swap partitions in /etc/fstab every time
you boot except if they are commented out (having ``#'' as the first
character in the line.)
Run free to check out the size of the swap space when you have
rebooted into Linux. You should also reboot into FreeBSD to make sure
everything works as expected. If it does not, you have probably used
the wrong partition as swap partition. The only solution to that
problem is to reinstall FreeBSD and try again. Experience is a great
teacher. :-)
4. Booting FreeBSD using LILO
You can easily boot FreeBSD with LILO. Do not install the FreeBSD boot
selector (Booteasy) if you want to use LILO. Append the following
lines to your /etc/lilo.conf file and run lilo (assuming the FreeBSD
slice is /dev/hda4):
other=/dev/hda4
table=/dev/hda
label=FreeBSD
If you have installed FreeBSD on the second SCSI drive, use something
like this (the FreeBSD slice being /dev/sdb2):
other=/dev/sdb2
table=/dev/sdb
loader=/boot/chain.b
label=FreeBSD
5. Mounting file systems
5.1. Mounting UFS file systems under Linux
Unfortunately the UFS driver in the Linux 2.0.xx kernels do not
include support for FreeBSD. When you try to mount a FreeBSD file
system, you just get some error messages (the file system actually
gets mounted, but you cannot read anything from it.) This problem has
been solved in Linux 2.1.87 and higher.
There is another version of the UFS driver for Linux 2.0.xx kernels
(xx <= 30) on SunSite . It
is called U2FS and the current version is u2fs-0.4.3.tar.gz. A version
of U2FS (ufs-0.4.4.tar.gz) for Linux 2.0.31 and higher (2.0.xx; not
2.1.xx) can be found at this site along with further information
about U2FS (and UFS.)
Now you have to build a new kernel with support for the U2FS file
system and BSD disklabels. See section ``Installing and preparing
Linux'' for more information on this. You can leave out UFS filesystem
support from the kernel when you use U2FS.
When you have installed the new kernel, you can mount your UFS file
systems (all the partitions in the FreeBSD slice except the swap
partition) with a command like this:
mount -t u2fs /dev/hda8 /mnt
You should use a command like
mount -t ufs /dev/hda8 /mnt
if you use a Linux kernel version 2.1.87 or higher.
The UFS (and U2FS) driver is read-only. That is; you can read from the
UFS file systems but you cannot write to them. Work on a read/write
driver has just begun.
5.2. Mounting ext2fs file systems under FreeBSD
To mount ext2fs file systems under FreeBSD, you first have to build a
new kernel with ext2fs support. Read the FreeBSD handbook
to learn how to do that. Put the
line
options "EXT2FS"
in your kernel configuration file for the new kernel.
When you have booted with the new kernel, you can mount an ext2fs file
system by giving a command like:
mount -t ext2fs /dev/wd0s3 /mnt
Note that you cannot mount ext2fs file systems in extended partitions
from FreeBSD.
Due to a bug in FreeBSD 2.2.5 and earlier you will have to unmount all
ext2fs file systems before you shut down FreeBSD if you are using
these versions. If you shut down FreeBSD with an ext2fs file system
mounted, FreeBSD cannot sync the UFS file systems. This results in
fsck being run the next time FreeBSD is booted.
6. Running foreign binaries
6.1. Running FreeBSD binaries under Linux
The iBCS package has support for running FreeBSD binaries under Linux;
but it's old and unmaintained. I can't get it to work. Please let me
know if you have had better luck with this.
6.2. Running Linux binaries under FreeBSD
FreeBSD has the ability to run Linux binaries, both in a.out and ELF
formats. To do this you have to take the following three steps:
1. You have to enable Linux compatibility. To do this (in FreeBSD
2.2.2 --- details may vary in other versions) you have to edit your
/etc/rc.conf file and change
linux_enable="NO"
to
linux_enable="YES"
and reboot. Another way to load the Linux binary support is to execute
the command /usr/bin/linux. This way you don't have to reboot, and you
don't always have the Linux binary support loaded (i.e. you save mem
ory.) Remember to add the line
options COMPAT_LINUX
to the FreeBSD kernel config file if you build a new FreeBSD kernel.
2. You have to install the Linux shared libraries if your Linux
binaries are dynamically linked. The libraries are included in
FreeBSD 2.2.{2,5,6} as the package linux_lib-2.4.tgz. Run the
following command to install the package:
pkg_add /linux_lib-2.4.tgz
is the directory where the package is stored. You
may also load it off the net by:
pkg_add ftp://ftp.freebsd.org/pub/FreeBSD/packages-stable/All/linux_lib-2.4.tgz
or by re-running /stand/sysinstall. Enter ``Configure'', ``Packages''
and use the menus. You should execute the following command if you are
running statically linked Linux binaries:
brandelf -t Linux
3. Install the Linux program(s) you want to run. The program(s) can be
installed on either UFS or ext2fs file systems. See section
``Mounting ext2fs file systems under FreeBSD'' for more information
about using ext2fs file systems under FreeBSD.
I have successfully run the Linux versions of Applixware 4.3 and
Netscape 3.01 (both ELF format) under FreeBSD 2.2.2 using this method
(yes, I know there is a native FreeBSD version of Netscape 4.) The
Linux versions of acroread and StarOffice also work well under
FreeBSD. Read the FreeBSD documentation for more information on this
topic.
7. References and other documents of interest
The latest version of this mini-HOWTO can be downloaded from my
homepage in several formats (including
SGML and PostScript.) The document has been translated into Japanese
by Mr. Teruyoshi Fujiwara as part of the JF project
.
Gregor Hoffleit maintains a homepage with information about the
developement of U2FS and UFS.
The FreeBSD Project Homepage has a lot of
information about FreeBSD (besides the whole system ready for
download.)
The Linux Kernel HOWTO is released as part of The Linux Documentation
Project .
8. Acknowledgments and Copyright
Thanks to the members of the *BSD user group in Denmark
for answering the questions of a
FreeBSD newbie, to Mr. Takeshi Okazaki for bringing the existence of
U2FS to my attention, and to Mr. David O'Brien for valuable
suggestions.
8.1. Disclaimer
Although the information given in this document is believed to be
correct, the authors will accept no liability for the content of this
document. Use the tips and examples given herein at your own risk.
8.2. Copyright
Copyright © 1997, 1998 by Niels Kristian Bech Jensen. This document
may be distributed only subject to the terms and conditions set forth
in the LDP license .