  The Linux+FreeBSD mini-HOWTO
  Niels Kristian Bech Jensen, nkbj@image.dk
  v1.4, 23 January 1998

  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. 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); 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''. The ``-current''
  development tree is where the development of new features is going on,
  while changes to the ``-stable'' tree 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 doesn't display
  the 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):

  # 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
  #

  The letters `a'...`f' in the first column are the same labels as shown
  below in the example for a FreeBSD slice. The letter `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 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 run dmesg in Linux you will see this as (The linux kernel must
  be build with UFS 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/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

  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 your
  in for trouble. Since 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. 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 (xx <= 30) 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

  Versions of U2FS for Linux kernels 2.0.31 and higher
  (u2fs-0.4.4.tar.gz) and for the latest 2.1.xx kernels can be found at
  this site <http://www.image.dk/~nkbj/u2fs/>.

  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

  Note that you cannot mount ext2fs file systems in extended partitions
  from FreeBSD.

  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 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"

  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.

  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 (c) 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 <http://sunsite.unc.edu/LDP/LICENSE.html>.

