compat_linux - setup for running Linux binaries under emulation
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 [Toc] [Back]
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
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 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 ldconfiglinux 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 [Toc] [Back]
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 [Toc] [Back]
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 [Toc] [Back]
Only the DSP device is emulated, the following link should
be created:
/emul/linux/dev/dsp -> /dev/audio
Other links Linux binaries may require [Toc] [Back]
CD-ROM support requires a link to the cdrom device, similar
to:
/emul/linux/dev/cdrom -> /dev/cd0a (first CD-ROM)
File systems [Toc] [Back]
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.
OpenBSD 3.6 March 2, 1995
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