NetBSD/share/man/man8/compat_linux.8

.\"	$NetBSD: compat_linux.8,v 1.16 2000/04/15 00:16:56 hubertf Exp $
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.Dd January 16, 1999
.Dt COMPAT_LINUX 8
.Os
.Sh NAME
.Nm compat_linux
.Nd setup procedure for running Linux binaries
.Sh DESCRIPTION
.Nx
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. Programs that
will not work include the Linux /proc filesystem (which is different from
the optional
.Nx
/proc filesystem), and i386-specific calls, such as
enabling virtual 8086 mode. Currently, sound is only partially
supported for Linux binaries (they will probably run, depending on
what Linux sound support features are used).

The Linux compatibility feature is active
for kernels compiled with the
.Dv COMPAT_LINUX
option enabled.
If support for Linux a.out executables is desired, the
.Dv EXEC_AOUT
option should be enabled in addition to
.Dv COMPAT_LINUX .
Similarly, if support for Linux 32-bit and/or 64-bit ELF executables
is desired, the
.Dv EXEC_ELF32
and/or
.Dv EXEC_ELF64
options (respectively) should be enabled in addition to
.Dv COMPAT_LINUX .
.Pp
A lot of programs are dynamically linked. This means, that you will
also need the Linux shared libraries that the program depends on, and
the runtime linker. Also, you will need to create a "shadow root"
directory for Linux binaries on your
.Nx
system. This directory
is named /emul/linux. Any file operations done by Linux programs
run under
.Nx
will look in this directory first. So, if a Linux
program opens, for example, /etc/passwd,
.Nx
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 you install
Linux packages that include configuration files, etc under /emul/linux,
to avoid naming conflicts with possible
.Nx
counterparts. Shared
libraries should also be installed in the shadow tree.
.Pp
Generally, you will need to look for the shared libraries that Linux
binaries depend on only the first few times that you install a Linux
program on your
.Nx
system. After a while, you will have a sufficient
set of Linux shared libraries on your 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 2 possibilities (when following
these instructions: you will need to be root on your
.Nx
system to
do the necessary installation steps).

.Bl -tag -width 123 -compact
.It 1.
You have access to a Linux system. In this case you can
temporarily install the binary there, see what shared libraries
it needs, and copy them to your
.Nx
system. Example: you have
just ftp-ed the Linux binary of Doom. Put it on the Linux
system you have access to, and check which shared libraries it
needs by running `ldd linuxxdoom':
.Pp
.Bl -tag -width 123 -compact -offset indent
.It (me@linux) ldd linuxxdoom
.nf
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
.fi
.El
.Pp
You would need go 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. This means you eventually have
these files on your
.Nx
system:
.Pp
.nf
/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)
.fi
.Pp
Note that if you already have a Linux shared library with a
matching major revision number to the first column of the 'ldd'
output, you won't need to copy the file named in the last column
to your system, the one you already have should work. It is
advisable to copy the shared library anyway if it is a newer version,
though. You can remove the old one, as long as you make the symbolic
link point to the new one. So, if you have these libraries
on your system:
.Pp
.nf
/emul/linux/lib/libc.so.4.6.27
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.27
.fi
.Pp
and you find that the ldd output for a new binary you want to
install is:
.nf
.Pp
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
.fi
.Pp
you won't need to worry about copying /lib/libc.so.4.6.29 too,
because the program should work fine with the slightly older version.
You can decide to replace the libc.so anyway, and that should leave
you with:
.Pp
.nf
/emul/linux/lib/libc.so.4.6.29
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.29
.fi
.Pp
Please note that the symbolic link mechanism is
.Em only
needed for Linux binaries, the
.Nx
runtime linker takes care of
looking for matching major revision numbers itself, you
don't need to worry about that.
.Pp
Finally, you must make sure that you have the Linux runtime linker
and its config files on your system. You should copy these
files from the Linux system to their appropriate place on your
.Nx
system (in the /emul/linux tree):
.Pp
.nf
/lib/ld.so
/etc/ld.so.cache
/etc/ld.so.config
.fi
.Pp
.It 2.
You don't have access to a Linux system. In that case, you
should get the extra files you need from various ftp sites.
Information on where to look for the various files is appended
below. For now, let's assume you know where to get the files.
.Pp
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):
.Pp
.nf
/sbin/ldconfig
/usr/bin/ldd
/lib/libc.so.x.y.z
/lib/ld.so
.fi
.Pp
ldconfig and ldd don't necessarily need to be under /emul/linux,
you can install them elsewhere in the system too. Just make sure
they don't conflict with their
.Nx
counterparts. A good idea
would be to install them in /usr/local/bin as ldconfig-linux and
ldd-linux.
.Pp
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, you could
add the following:
.Pp
.nf
/usr/X11/lib
/usr/local/lib
.fi
.Pp
Note that these are mapped to /emul/linux/XXXX by
.Nx Ns 's
compat
code, and should exist as such on your 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
You should rerun the Linux version of the ldconfig program
each time you add a new shared library.
.Pp
You should now be set up for Linux binaries which only need
a shared libc. You can test this by running the Linux ldd
on itself. Suppose that you have it installed as ldd-linux, it
should produce something like:
.Pp
.Bl -tag -width 123 -compact -offset indent
.It (me@netbsd) ldd-linux `which ldd-linux`
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
.El
.Pp
This being done, you are ready to install new Linux binaries.
Whenever you install a new Linux program, you should check
if it needs shared libraries, and if so, whether you have
them installed in the /emul/linux tree. To do this, you run
the Linux version ldd on the new program, and watch its output.
ldd (see also the manual page for
.Xr 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" in stead of <fullname> it means that
you need an extra library. Which library this is, is shown
in <majorname>, which will be of the form libXXXX.so.<N>
You will need to find a libXXXX.so.<N>.<mm> on a Linux ftp site,
and install it on your 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.
.Pp
.It 3.
For i386, you can simply install the SuSE shared libs using the
.Pa pkgsrc/emulators/suse_linux
package(s).
.El
.Ss Setting up other files
Newer version of Linux use /etc/nsswitch.conf for network information,
such as
.Tn NIS
and DNS. You must create or get a valid copy of this file
and put it in /emul/linux/etc.

.Ss Finding the necessary files.
[
.Em Note:
As of October, 1998, a reasonable set of Linux libraries and other files
needed for Linux emulation may be obtained from
.Dl ftp://ftp.freebsd.org/pub/FreeBSD/distfiles/linux_lib-2.5.tar.gz
It is recommended you try to retrieve this file (or a more recent
version) from ftp.freebsd.org first as this tar file contains
everything one typically needs and is is very simple to use for this
application. Failing that, see the instructions below.
]
.Pp
.Em Note:
the information below is valid as of the time this
document was written (March, 1995), but certain details
such as names of ftp sites, directories and distribution names
may have changed by the time you read this.
.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 you can get the individual files you need, 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:
.Pp
.nf
sunsite.unc.edu:/pub/Linux/distributions
tsx-11.mit.edu:/pub/linux/distributions
.fi
.Pp
Some European mirrors:
.Pp
.nf
ftp.luth.se:/pub/linux/distributions
ftp.demon.co.uk:/pub/linux/distributions
src.doc.ic.ac.uk:/packages/linux/distributions
.fi
.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 you can
retrieve files "by hand" too. First of all, you will need to look
in the "contents" subdir of the distribution. You will find
a lot of small textfiles here describing the contents of the separate
packages. The fastest way to look something up is to retrieve all
the files in the contents subdirectory, and grep through them for the file
you need. Here is an example of a list of files that you might need, and
in which contents-file you will find it by grepping through them:
.Pp
.Bd -unfilled -offset indent
Needed                  Package

ld.so                   ldso
ldconfig                ldso
ldd                     ldso
libc.so.4               shlibs
libX11.so.6.0           xf_lib
libXt.so.6.0            xf_lib
libX11.so.3             oldlibs
libXt.so.3              oldlibs
.Ed
.Pp
So, in this case, you will need the packages ldso, shlibs, xf_lib and oldlibs.
In each of the contents-files for these packages, look for a line saying
"PACKAGE LOCATION", it will tell you on which 'disk' the package is,
in our case it will tell us in which subdirectory we need to look.
For our example, we would find the following locations:
.Pp
.Bd -unfilled -offset indent
Package                 Location

ldso                    diska2
shlibs                  diska2
oldlibs                 diskx6
xf_lib                  diskx9
.Ed
.Pp
The locations called "diskXX" refer to the "slakware/XX" subdirectories
of the distribution, others may be found in the "contrib" subdirectory.
In this case, we could now retrieve the packages we need by retrieving
the following files (relative to the root of the Slackware distribution
tree):
.Pp
.nf
slakware/a2/ldso.tgz
slakware/a2/shlibs.tgz
slakware/x6/oldlibs/tgz
slakware/x9/xf_lib.tgz
.fi
.Pp
Extract the files from these gzipped tarfiles in your /emul/linux directory
(possibly omitting or afterwards removing files you don't need), and you
are done.

.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 you will also have to create
some symbloic links in the /emul/linux/dev directory, namely:
.Pp
.nf
/emul/linux/dev/console -> /dev/tty
/emul/linux/dev/mouse -> whatever device your mouse is connected to
/emul/linux/dev/ttyS0 -> /dev/tty00
/emul/linux/dev/ttyS1 -> /dev/tty01
.fi
.Pp
Be warned: the first link mentioned here makes SVGAlib binaries
work, but may confuse others, so you may have to remove it again at
some point.
.Sh BUGS
The information about Linux distributions may become outdated.
.Pp
Pathnames pointed to by symbolic links are not looked up in the
shadow root when running a Linux executable. This is not consistent.
.Pp
Linux executables can not handle directory offset cookies > 32 bits.
Should such an offset occur, you will see the message "linux_getdents:
dir offset too large for emulated program". Currently, this can only
happen on NFS mounted filesystems, mounted from servers that return
offsets with information in the upper 32 bits. These errors should 
rarely happen, but can be avoided by mounting this filesystem with offset
translation enabled. See the
.Fl X
option to
.Xr mount_nfs 8 .
The
.Fl 2
option to
.Xr mount_nfs 8
will also have the desired effect, but is less preferable.