COMPAT_LINUX(8) BSD System Manager's Manual COMPAT_LINUX(8)
compat_linux - setup for running Linux binaries under emulation
OpenBSD supports running Linux binaries. This only applies to i386 sys-
tems for now. Both the a.out and ELF binary formats are supported. Most
programs should work, including the ones that use the Linux SVGAlib. Ad-
ditionally, OSS audio is emulated, so Linux binaries can access the na-
tive audio transparently. Programs that will not work include those that
use i386-specific calls, such as enabling virtual 8086 mode.
The Linux compatibility feature is active for kernels compiled with the
COMPAT_LINUX option and kern.emul.linux sysctl(8) enabled. The default OS
type is set to the host OS type, usually MirBSD, but can be changed via
the kern.emul_uname sysctl.
A lot of programs are dynamically linked. This means that the Linux
shared libraries that the programs depend on and the runtime linker are
also needed. Additionally, a "shadow root" directory for Linux binaries
on the OpenBSD system will have to be created. This directory is named
/emul/linux. Any file operations done by Linux programs run under OpenBSD
will look in this directory first. So, if a Linux program opens, for ex-
ample, /etc/passwd, OpenBSD will first try to open
/emul/linux/etc/passwd, and if that does not exist open the `real'
/etc/passwd file. It is recommended that Linux packages that include con-
figuration files, etc., be installed under /emul/linux, to avoid naming
conflicts with possible OpenBSD counterparts. Shared libraries should
also be installed in the shadow tree.
Generally, it will only be necessary to look for the shared libraries
that Linux binaries depend on the first few times that Linux programs are
installed on the OpenBSD system. After a while, there will be a suffi-
cient set of Linux shared libraries on the system to be able to run newly
imported Linux binaries without any extra work.
How to get to know which shared libraries Linux binaries need, and where
to get them? Basically, there are 3 possibilities. (When following these
instructions, root privileges are required on the OpenBSD system to per-
form the necessary installation steps).
1. Access to the OpenBSD ports(7) system: Install the port named
redhat/base in the emulators category. The redhat/base port contains
the shared libraries, binaries, and other related files necessary to
run Linux applications. Access to a Linux system is not needed.
2. Access to a Linux system: In this case temporarily install the
binary there, see what shared libraries it needs, and copy them to
the OpenBSD system. Example: ftp the Linux binary of Doom. Put it on
the Linux system, and check which shared libraries it needs by run-
ning `ldd linuxxdoom':
(me@linux) ldd linuxxdoom
libXt.so.3 (DLL Jump 3.1) => /usr/X11/lib/libXt.so.3.1.0
libX11.so.3 (DLL Jump 3.1) => /usr/X11/lib/libX11.so.3.1.0
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
Get all the files from the last column, and put them under
/emul/linux, with the names in the first column as symbolic links
pointing to them. The following files would therefore be required on
the OpenBSD system:
/emul/linux/usr/X11/lib/libXt.so.3.1.0
/emul/linux/usr/X11/lib/libXt.so.3 (symbolic link to the above)
/emul/linux/usr/X11/lib/libX11.so.3.1.0
/emul/linux/usr/X11/lib/libX11.so.3 (symbolic link to the above)
/emul/linux/lib/libc.so.4.6.29
/emul/linux/lib/libc.so.4 (symbolic link to the above)
Note that if a Linux shared library with a matching major revision
number to the first column of the 'ldd' output is already present,
it isn't necessary to copy the file named in the last column to the
OpenBSD system; the one already there should work. It is advisable
to copy the shared library anyway, if it is a newer version. The old
one can be removed, as long as the symbolic link points to the new
one. So, if these libraries exist on the system:
/emul/linux/lib/libc.so.4.6.27
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.27
and the ldd output for a new binary is:
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
it isn't necessary to copy /lib/libc.so.4.6.29 too, because the pro-
gram should work fine with the slightly older version. libc.so can
be replaced anyway, and that should leave:
/emul/linux/lib/libc.so.4.6.29
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.29
Please note that the symbolic link mechanism is only needed for
Linux binaries, the OpenBSD runtime linker takes care of looking for
matching major revision numbers itself.
Finally, the Linux runtime linker and its config files must be
present on the system. These files should be copied from the Linux
system to their appropriate place on the OpenBSD system (in the
/emul/linux tree):
/lib/ld.so
/etc/ld.so.cache
/etc/ld.so.config
3. No access to a Linux system: In that case, get the extra files from
various ftp sites. Information on where to look for the various
files is appended below.
Retrieve the following files (from _one_ ftp site to avoid any ver-
sion mismatches), and install them under /emul/linux (i.e. /foo/bar
is installed as /emul/linux/foo/bar):
/sbin/ldconfig
/usr/bin/ldd
/lib/libc.so.x.y.z
/lib/ld.so
ldconfig and ldd don't necessarily need to be under /emul/linux,
they can be installed elsewhere in the system too. Just make sure
they don't conflict with their OpenBSD counterparts. A good idea
would be to install them in /usr/local/bin as ldconfig-linux and
ldd-linux.
Create the file /emul/linux/etc/ld.so.conf, containing the direc-
tories in which the Linux runtime linker should look for shared
libs. It is a plain text file, containing a directory name on each
line. /lib and /usr/lib are standard; the following could be added:
/usr/X11/lib
/usr/local/lib
Note that these are mapped to /emul/linux/XXXX by the OpenBSD compat
code, and should exist as such on the OpenBSD system.
Run the Linux ldconfig program. It should be statically linked, so
it doesn't need any shared libraries by itself. It will create the
file /emul/linux/etc/ld.so.cache. The Linux version of the ldconfig
program should be rerun each time a new shared library is added.
The OpenBSD system should now be set up for Linux binaries which
only need a shared libc. Test this by running the Linux ldd on it-
self. Suppose that it is installed as ldd-linux, it should produce
something like:
% ldd-linux `which ldd-linux`
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
This being done, new Linux binaries can now be installed. Whenever a
new Linux program is installed, it should be determined if it needs
shared libraries, and if so, whether they are installed in the
/emul/linux tree. To do this, run the Linux version ldd on the new
program, and watch its output. ldd (see also the manual page for
ldd(1)) will print a list of shared libraries that the program
depends on, in the form <majorname> (<jumpversion>) => <fullname>.
If it prints "not found" instead of <fullname> it means that an ex-
tra library is needed. Which library this is, is shown in <major-
name>, which will be of the form libXXXX.so.<N>. Find a
libXXXX.so.<N>.<mm> on a Linux ftp site, and install it on the
OpenBSD system. The XXXX (name) and <N> (major revision number)
should match; the minor number(s) <mm> are less important, though it
is advised to take the most recent version.
Note: the information below is valid as of Feb 2003, but certain details
such as names of ftp sites, directories and distribution names may have
changed since then. It is much easier to use the OpenBSD ports(7) system
(possibility 1, above).
Linux is distributed by several groups that make their own set of
binaries that they distribute. Each distribution has its own name, like
"Slackware" or "Yggdrasil". The distributions are available on a lot of
ftp sites. Sometimes the files are unpacked, and individual files can be
retrieved, but mostly they are stored in distribution sets, usually con-
sisting of subdirectories with gzipped tar files in them. The primary ftp
sites for the distributions are:
ftp.ibiblio.org:/pub/Linux/distributions
distro.ibiblio.org:/pub/Linux/distributions
Some European mirrors:
ftp.sunet.se:/pub/Linux/distributions
src.doc.ic.ac.uk:/packages/linux
For simplicity, let's concentrate on Slackware here. This distribution
consists of a number of subdirectories, containing separate packages.
Normally, they're controlled by an install program, but the files can be
retrieved "by hand" too. The fastest way to find something is to grep(1)
the file FILELIST.TXT for the files needed. Here is an example of a list
of files that might be needed, and in which package it can be found:
Needed Package
ld-2.2.5.so glibc
ldconfig glibc
ldd glibc
libc.so.6 glibc
libX11.so.6 xfree
libXt.so.6 xfree
So, in this case, the packages glibc and xfree will be needed.
FILELIST.TXT also gives the location of the packages. Retrieve the pack-
ages needed from the following files (relative to the root of the
Slackware distribution tree):
slackware/l/glibc-2.2.5-i386.2.tgz
slackware/x/xfree-4.2.0-i386.5.tgz
Extract the files from these gzipped tarfiles in the /emul/linux directo-
ry (possibly omitting or afterwards removing unnecessary files).
SVGAlib binaries require some extra care. The pcvt virtual console driver
has to be in the kernel for them to work, and some symbolic links in the
/emul/linux/dev directory will have to be created, namely:
/emul/linux/dev/console -> /dev/tty
/emul/linux/dev/mouse -> whatever device the mouse is connected to
/emul/linux/dev/ttyS0 -> /dev/tty00
/emul/linux/dev/ttyS1 -> /dev/tty01
Be warned: the first link mentioned here makes SVGAlib binaries work, but
may confuse others, so it may be necessary to remove it again at some
point.
Only the DSP device is emulated, the following link should be created:
/emul/linux/dev/dsp -> /dev/audio
CD-ROM support requires a link to the CD-ROM device, similar to:
/emul/linux/dev/cdrom -> /dev/cd0a (first CD-ROM)
Many Linux binaries expect /proc to have procfs mounted on it. Some
binaries will require it to be mounted using the -o linux option.
The information about Linux distributions may become outdated.
Linux ELF binaries may be detected as SVR4 binaries. This can usually be
fixed with elf2olf(1) by setting the OLF opsys tag to Linux, e.g.
% elf2olf -o linux <linux_binary>
compat_linux is currently only supported on the i386.
MirBSD #10-current March 2, 1995 3