COMPAT_LINUX(8) OpenBSD System Manager's Manual COMPAT_LINUX(8)NAMEcompat_linux - setup for running Linux binaries under emulation
DESCRIPTION
OpenBSD supports running Linux binaries. This only applies to i386
systems for now. Both the a.out and ELF binary formats are supported.
Most programs should work, including the ones that use the Linux SVGAlib.
Additionally, OSS audio is emulated, so Linux binaries can access the
native 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.
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 example, /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
configuration 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
sufficient set of Linux shared libraries on the system to be able to run
newly imported Linux binaries without any extra work.
Setting up shared libraries
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
perform the necessary installation steps).
1. Access to the OpenBSD ports(7) system: Install the port named
fedora/base in the emulators category. The fedora/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
running `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
program 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
version 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
directories 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
itself. 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
extra library is needed. Which library this is, is shown in
<majorname>, 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.
Finding the necessary files
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
consisting 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
packages 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
directory (possibly omitting or afterwards removing unnecessary files).
Programs using SVGAlib
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.
Programs using OSS (Linux) audio
Only the DSP device is emulated, the following link should be created:
/emul/linux/dev/dsp -> /dev/audio
Other links Linux binaries may require
CD-ROM support requires a link to the CD-ROM device, similar to:
/emul/linux/dev/cdrom -> /dev/cd0a (first CD-ROM)
File systems
Many Linux binaries expect /proc to have procfs mounted on it. Some
binaries will require it to be mounted using the -o linux option.
BUGS
The information about Linux distributions may become outdated.
compat_linux is currently only supported on the i386.
OpenBSD 4.9 October 22, 2009 OpenBSD 4.9
