The Linux+FreeBSD mini-HOWTO
Niels Kristian Bech Jensen, nkbj@image.dk
v1.1, 3 October 1997
This document describes how to use Linux and FreeBSD on the same sys�
tem. It introduces FreeBSD and discuss how the two operating systems
can interact, e.g. by sharing swap space. You should probably have
some experience with Linux and hard drive partitioning (fdisk) before
you read this document. Do not hesitate to mail me if you have com�
ments, questions or suggestions about this document. I would also like
to hear from people who have experience using Linux together with
NetBSD or OpenBSD.
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. FreeBSD
runs only on the Intel PC platform (i386 and higher); a port to the
DEC Alpha platform is being discussed at the moment. Hardware
requirements for FreeBSD are much like those for Linux.
The development of FreeBSD is more ``closed'' than the Linux
development. A core team of developers makes the key decisions
concerning 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''. ``-current'' is where the
development of new features is going on, while development of the
``-stable'' releases mainly are bug fixes.
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 FreeBSD Inc. <http://www.freebsd.org/>. The newest
``-stable'' releases and snapshots of the ``-current'' development
code are sold on CDROMs by Walnut Creek CDROM <http://www.cdrom.com/>
(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.
2.1. FreeBSD ``slices'' and ``partitions''
FreeBSD needs only one entry in the primary partition table on your
hard drive. This primary partition is called a ``slice'' in FreeBSD
terminology. It then uses the program disklabel to make several
logical 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. Note that the Linux fdisk program can't display
the partitions in a FreeBSD slice, the output is something like this
(/dev/hda4 is the FreeBSD slice):
hafnium:~# 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 28 375 701568 83 Linux native
/dev/hda3 376 376 403 56448 83 Linux native
/dev/hda4 404 404 621 439488 a5 BSD/386
Command (m for help): q
hafnium:~#
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 a 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 a FreeBSD slice is labelled in the following way
(/dev/hda4 is the FreeBSD slice in the example):
Linux label FreeBSD label Default FreeBSD mount point
/dev/hda5 /dev/wd0s4a /
/dev/hda6 /dev/wd0s4b swap
/dev/hda7 /dev/wd0s4e /var
/dev/hda8 /dev/wd0s4f /usr
If you have installed FreeBSD in the /dev/sdb3 slice, 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 Default FreeBSD mount point
/dev/sdb7 /dev/sd1s3a /
/dev/sdb8 /dev/sd1s3b swap
/dev/sdb9 /dev/sd1s3e /var
/dev/sdb10 /dev/sd1s3f /usr
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. This is
based on Red Hat Linux release 4.1 and 4.2 (Linux kernel 2.0.29 and
2.0.30) and FreeBSD 2.2.2. 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 you 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 UFS file
system support 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 disk with the new
kernel. You are now ready to install FreeBSD.
3.2. Installing FreeBSD
Install FreeBSD as described in the FreeBSD documentation. Remove the
Linux swap partition is 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 disk.
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 /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
loader (Booteasy) if you want to use LILO. Append the following lines
to your /etc/lilo.conf file and run lilo (the FreeBSD slice being
/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 support in the Linux kernel is broken. When you
try to mount a UFS file system, you just get some error messages (the
file system actually gets mounted, but you cannot read anything from
it.)
However, there is a new (ALPHA) version of the UFS file system support
for Linux 2.0.xx kernels on SunSite
<ftp://sunsite.unc.edu/pub/Linux/ALPHA/ufs/>. It is called U2FS and
the current version is u2fs-0.4.3.tar.gz. U2FS is installed in the
following way (assuming u2fs-0.4.3.tar.gz is stored in /usr/src):
cd /usr/src
tar xvzf u2fs-0.4.3.tar.gz
patch -p0 -E < u2fs-0.4.3.patch
Now you have to build a new kernel with support for the U2FS file
system and BSD disklabel. See section ``Installing and preparing
Linux'' for more information on this. You can leave out UFS file
system 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
The UFS support is read-only. That is; you can read from the UFS file
systems but you cannot write to them.
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 documentation 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
Due to a bug in FreeBSD you will have to unmount all ext2fs file
systems before you shut down FreeBSD. 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. This
bug is reported to have been fixed in the ``-current'' development
tree.
6. 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"
2. You have to install the Linux shared libraries. They are included
in FreeBSD 2.2.2 as the package linux_lib-2.4.tgz (a newer version
might be out now.) Run the command
pkg_add <path_to_package>/linux_lib-2.4.tgz
to install the package. <path_to_package> is the directory where the
package is stored.
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.) Read
the FreeBSD documentation for more information on this topic.
7. References and other documents of interest
The newest version of this mini-HOWTO can be found at my homepage
<http://www.image.dk/~nkbj/> in several formats (including SGML and
PostScript.) The document has been translated into Japanese by Mr.
Teruyoshi Fujiwara as part of the JF project
<ftp://jf.linux.or.jp/pub/JF/other-formats/>.
The FreeBSD Handbook and The FreeBSD FAQ are distributed with FreeBSD.
They can also be found at FreeBSD Inc. <http://www.freebsd.org/>.
This site has a lot of other information about FreeBSD too.
The Linux Kernel HOWTO is released as part of The Linux Documentation
Project <http://sunsite.unc.edu/LDP/>.
8. Acknowledgments and Copyright
Thanks to the members of the *BSD user group in Denmark
<http://hotel.prosa.dk/bsd-dk/> for answering the questions of a
FreeBSD newbie and to Mr. Takeshi Okazaki for bringing the existence
of U2FS to my attention.
This document is copyrighted by Niels Kristian Bech Jensen,
nkbj@image.dk. It is distributed as part of The Linux Documentation
Project <http://sunsite.unc.edu/LDP/> under the terms described below.
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If you have questions, please contact Greg Hankins, the Linux HOWTO
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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.