OpenBSD-4.6/share/man/man8/compat_linux.8

.\"	$OpenBSD: compat_linux.8,v 1.39 2008/06/06 15:17:48 jmc Exp $
.\"	$NetBSD: compat_linux.8,v 1.2 1995/10/16 20:17:59 fvdl Exp $
.\"
.\" Copyright (c) 1995 Frank van der Linden
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.\"
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.\"    must display the following acknowledgement:
.\"      This product includes software developed for the NetBSD Project
.\"      by Frank van der Linden
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.\"    derived from this software without specific prior written permission
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.Dd $Mdocdate: June 6 2008 $
.Dt COMPAT_LINUX 8
.Os
.Sh NAME
.Nm compat_linux
.Nd setup for running Linux binaries under emulation
.Sh DESCRIPTION
.Ox
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.
.Pp
The Linux compatibility feature is active
for kernels compiled with the
.Nm COMPAT_LINUX
option and kern.emul.linux
.Xr sysctl 8
enabled.
.Pp
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
.Ox
system will have to be created.
This directory is named
.Pa /emul/linux .
Any file operations done by Linux programs run under
.Ox
will look in this directory first.
So, if a Linux program opens, for example,
.Pa /etc/passwd ,
.Ox
will first try to open
.Pa /emul/linux/etc/passwd ,
and if that does not exist open the `real'
.Pa /etc/passwd
file.
It is recommended that Linux packages that include configuration
files, etc., be installed under
.Pa /emul/linux ,
to avoid naming conflicts with possible
.Ox
counterparts.
Shared libraries should also be installed in the shadow tree.
.Pp
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
.Ox
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.
.Ss 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
.Ox
system to perform the necessary installation steps).
.Bl -enum
.It
Access to the
.Ox
.Xr ports 7
system:
Install the port named
.Nm fedora/base
in the
.Nm emulators
category.
The
.Nm 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.
.It
Access to a Linux system:
In this case temporarily install the binary there, see what
shared libraries it needs, and copy them to the
.Ox
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':
.Pp
.Dl (me@linux) ldd linuxxdoom
.Bd -unfilled -offset indent
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
.Ed
.Pp
Get all the files from the last column, and put them under
.Pa /emul/linux ,
with the names in the first column
as symbolic links pointing to them.
The following files would therefore be required on the
.Ox
system:
.Bd -unfilled -offset indent
/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)
.Ed
.Pp
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
.Ox
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:
.Bd -unfilled -offset indent
/emul/linux/lib/libc.so.4.6.27
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.27
.Ed
.Pp
and the ldd output for a new binary is:
.Bd -unfilled -offset indent
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
.Ed
.Pp
it isn't necessary to copy
.Pa /lib/libc.so.4.6.29
too, because the program should work fine with the slightly older version.
.Pa libc.so
can be replaced anyway, and that should leave:
.Bd -unfilled -offset indent
/emul/linux/lib/libc.so.4.6.29
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.29
.Ed
.Pp
Please note that the symbolic link mechanism is
only needed for Linux binaries, the
.Ox
runtime linker takes care of looking for matching major revision numbers
itself.
.Pp
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
.Ox
system (in the
.Pa /emul/linux
tree):
.Bd -unfilled -offset indent
/lib/ld.so
/etc/ld.so.cache
/etc/ld.so.config
.Ed
.It
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.
.Pp
Retrieve the following files (from _one_ ftp site to avoid
any version mismatches), and install them under
.Pa /emul/linux
(i.e.\&
.Pa /foo/bar
is installed as
.Pa /emul/linux/foo/bar ) :
.Bd -unfilled -offset indent
/sbin/ldconfig
/usr/bin/ldd
/lib/libc.so.x.y.z
/lib/ld.so
.Ed
.Pp
ldconfig and ldd don't necessarily need to be under
.Pa /emul/linux ,
they can be installed elsewhere in the system too.
Just make sure they don't conflict with their
.Ox
counterparts.
A good idea would be to install them in
.Pa /usr/local/bin
as ldconfig-linux and ldd-linux.
.Pp
Create the file
.Pa /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.
.Pa /lib
and
.Pa /usr/lib
are standard; the following could be added:
.Bd -unfilled -offset indent
/usr/X11/lib
/usr/local/lib
.Ed
.Pp
Note that these are mapped to
.Pa /emul/linux/XXXX
by the
.Ox
compat code, and should exist as such on the
.Ox
system.
.Pp
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
.Pa /emul/linux/etc/ld.so.cache .
The Linux version of the ldconfig program should be rerun
each time a new shared library is added.
.Pp
The
.Ox
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:
.Pp
.Dl % ldd-linux `which ldd-linux`
.Pp
.D1 libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
.Pp
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
.Pa /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>.
.Pp
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
.Ox
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.
.El
.Ss Finding the necessary files
.Sy 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
.Ox
.Xr ports 7
system (possibility 1, above).
.Pp
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:
.Bd -unfilled -offset indent
.Pa ftp.ibiblio.org:/pub/Linux/distributions
.Pa distro.ibiblio.org:/pub/Linux/distributions
.\" .Pa tsx-11.mit.edu:/pub/linux/distributions
.Ed
.Pp
Some European mirrors:
.Bd -unfilled -offset indent
.\" .Pa ftp.luth.se:/pub/linux/distributions
.\" .Pa ftp.demon.co.uk:/pub/linux/distributions
.Pa ftp.sunet.se:/pub/Linux/distributions
.Pa src.doc.ic.ac.uk:/packages/linux
.Ed
.Pp
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
.Xr 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:
.Bd -unfilled -offset indent
Needed                  Package

ld-2.2.5.so             glibc
ldconfig                glibc
ldd                     glibc
libc.so.6               glibc
libX11.so.6             xfree
libXt.so.6              xfree
.Ed
.Pp
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):
.Bd -unfilled -offset indent
slackware/l/glibc-2.2.5-i386.2.tgz
slackware/x/xfree-4.2.0-i386.5.tgz
.Ed
.Pp
Extract the files from these gzipped tarfiles in the
.Pa /emul/linux
directory
(possibly omitting or afterwards removing unnecessary files).
.Ss 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
.Pa /emul/linux/dev
directory will have to be created, namely:
.Bd -unfilled -offset indent
/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
.Ed
.Pp
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.
.Ss Programs using OSS (Linux) audio
Only the DSP device is emulated, the following link should be created:
.Pp
.D1 /emul/linux/dev/dsp -> /dev/audio
.Ss Other links Linux binaries may require
CD-ROM support requires a link to the CD-ROM device, similar to:
.Pp
.D1 /emul/linux/dev/cdrom -> /dev/cd0a   (first CD-ROM)
.Ss File systems
Many Linux binaries expect
.Pa /proc
to have procfs mounted on it.
Some binaries will require it to be mounted using the
.Fl o Ar linux
option.
.Sh BUGS
The information about Linux distributions may become outdated.
.Pp
.Nm
is currently only supported on the i386.