man/man8/compat_linux.8

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.Dd September 29, 2017
.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 applies to amd64, arm, alpha, i386, m68k, and powerpc 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 (only
on i386).
.Nx
amd64 can execute both 32bit and 64bit linux programs.
Programs that will not work include some that use
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).
.Pp
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 option
.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
.Dq shadow root
directory for Linux binaries on your
.Nx
system.
This directory is named
.Pa /emul/linux
or
.Pa /emul/linux32
for 32bit emulation on 64bit systems.
Any file operations done by Linux programs run under
.Nx
will look in this directory first.
So, if a Linux program opens, for example,
.Pa /etc/passwd ,
.Nx
will
first try to open
.Pa /emul/linux/etc/passwd ,
and if that does not exist open the
.Sq real
.Pa /etc/passwd
file.
It is recommended that you install
Linux packages that include configuration files, etc under
.Pa /emul/linux ,
to avoid naming conflicts with possible
.Nx
counterparts.
Shared libraries should also be installed in the shadow tree.
Filenames that start "/../" are only looked up in the real root.
.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 -enum
.It
For i386, you can simply install the SuSE shared libs using the
.Pa pkgsrc/emulators/suse100_linux
package(s).
On PowerPC ports, the
.Pa pkgsrc/emulators/linuxppc_lib
will install the needed libraries.
If you are on other platforms, or this doesn't supply you with all
the needed libraries, read on.
.It
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
.Sq ldd linuxxdoom :
.Bd -literal -offset indent
(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
.Ed
.Pp
You would need go 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.
This means you eventually have these files on your
.Nx
system:
.Bl -item -compact
.It
.Pa /emul/linux/usr/X11/lib/libXt.so.3.1.0
.It
.Pa /emul/linux/usr/X11/lib/libXt.so.3
(symbolic link to the above)
.It
.Pa /emul/linux/usr/X11/lib/libX11.so.3.1.0
.It
.Pa /emul/linux/usr/X11/lib/libX11.so.3
(symbolic link to the above)
.It
.Pa /emul/linux/lib/libc.so.4.6.29
.It
.Pa /emul/linux/lib/libc.so.4
(symbolic link to the above)
.El
.Pp
Note that if you already have a Linux shared library with a
matching major revision number to the first column of the
.Xr ldd 1
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
.Bl -item -compact
.It
.Pa /emul/linux/lib/libc.so.4.6.27
.It
.Pa /emul/linux/lib/libc.so.4
->
.Pa /emul/linux/lib/libc.so.4.6.27
.El
.Pp
and you find that the
.Ic ldd
output for a new binary you want to install is:
.Bd -literal
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
.Ed
.Pp
you won't need to worry about copying
.Pa /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:
.Bl -item -compact
.It
.Pa /emul/linux/lib/libc.so.4.6.29
.It
.Pa /emul/linux/lib/libc.so.4
->
.Pa /emul/linux/lib/libc.so.4.6.29
.El
.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
.Pa /emul/linux
tree):
.Bl -item -compact
.It
.Pa /lib/ld.so
.It
.Pa /etc/ld.so.cache
.It
.Pa /etc/ld.so.config
.El
.It
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
.Pa /emul/linux
(i.e.
.Pa /foo/bar
is installed as
.Pa /emul/linux/foo/bar ) :
.Pp
.Bl -item -compact
.It
.Pa /sbin/ldconfig
.It
.Pa /usr/bin/ldd
.It
.Pa /lib/libc.so.x.y.z
.It
.Pa /lib/ld.so
.El
.Pp
.Ic ldconfig
and
.Ic ldd
don't necessarily need to be under
.Pa /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
.Pa /usr/local/bin
as
.Ic ldconfig-linux
and
.Ic 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, you could add the following:
.Bl -item -compact
.It
.Pa /usr/X11/lib
.It
.Pa /usr/local/lib
.El
.Pp
Note that these are mapped to
.Pa /emul/linux/XXXX
by
.Nx Ap s
compat
code, and should exist as such on your system.
.Pp
Run the Linux
.Ic 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
You should rerun the Linux version of
.Ic ldconfig
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
.Ic ldd
on itself.
Suppose that you have it installed as
.Ic 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
.Pa /emul/linux
tree.
To do this, you run the Linux
.Ic ldd
on the new program, and watch its output.
.Ic 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
.Aq majorname
.Pq Aq jumpversion
=>
.Aq fullname .
.Pp
If it prints
.Dq not found
instead of
.Aq fullname
it means that you need an extra library.
Which library this is, is shown in
.Aq 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
.Aq N
(major revision number) should match; the minor number(s)
.Aq mm
are less important, though it is advised to take the most recent version.
.It
Set up linux specific devices:
.Pp
.Bl -tag -width 123 -compact -offset indent
.It (me@netbsd) cd /usr/share/examples/emul/linux/etc
.br
.It (me@netbsd) cp LINUX_MAKEDEV /emul/linux/dev
.br
.It (me@netbsd) cd /emul/linux/dev && sh LINUX_MAKEDEV all
.El
.El
.Ss Setting up procfs
Some Linux binaries expect procfs to be mounted and that it would
contain some Linux specific stuff.
If it's not the case, they behave unexpectedly or even crash.
.Pp
Mount procfs on
.Nx
using following command:
.Bl -tag -width 123 -offset indent
.It (me@netbsd) mount_procfs -o linux procfs /emul/linux/proc
.El
.Pp
You can also set up your system so that procfs is mounted automatically
on system boot, by putting an entry like the one below to
.Pa /etc/fstab .
.Bl -tag -width 123 -offset indent
.It procfs /emul/linux/proc procfs ro,linux
.El
.Pp
See
.Xr mount_procfs 8
for further information.
.Ss Setting up other files
Newer version of Linux use
.Pa /etc/nsswitch.conf
for network information, such as NIS and DNS.
You must create or get a valid copy of this file and put it in
.Pa /emul/linux/etc .
.Ss Finding the necessary files
.Em Note :
the information below is valid as of the time this
document was first 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
.Dq Slackware
or
.Dq 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:
.Bl -item -compact -offset indent
.It
.Pa sunsite.unc.edu:/pub/Linux/distributions
.It
.Pa tsx-11.mit.edu:/pub/linux/distributions
.El
.Pp
Some European mirrors:
.Bl -item -compact -offset indent
.It
.Pa ftp.luth.se:/pub/linux/distributions
.It
.Pa ftp.demon.co.uk:/pub/linux/distributions
.It
.Pa src.doc.ic.ac.uk:/packages/linux/distributions
.El
.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
.Dq by hand
too.
First of all, you will need to look in the
.Pa 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:
.Bd -literal -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
.Dq PACKAGE LOCATION ,
it will tell you on which
.Sq 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:
.Bd -literal -offset indent
Package                 Location

ldso                    diska2
shlibs                  diska2
oldlibs                 diskx6
xf_lib                  diskx9
.Ed
.Pp
The locations called
.Pa diskXX
refer to the
.Pa slakware/XX
subdirectories
of the distribution, others may be found in the
.Pa 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):
.Bl -item -compact
.It
.Pa slakware/a2/ldso.tgz
.It
.Pa slakware/a2/shlibs.tgz
.It
.Pa slakware/x6/oldlibs/tgz
.It
.Pa slakware/x9/xf_lib.tgz
.El
.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.
You need to have
.Cd options WSDISPLAY_COMPAT_USL
in your kernel (see
.Xr wscons 4 ) ,
and you will also have to create
some symbolic links in the
.Pa /emul/linux/dev
directory, namely:
.Bl -item -compact
.It
.Pa /emul/linux/dev/console
->
.Pa /dev/tty
.It
.Pa /emul/linux/dev/mouse
-> whatever device your mouse is connected to
.It
.Pa /emul/linux/dev/ttyS0
->
.Pa /dev/tty00
.It
.Pa /emul/linux/dev/ttyS1
->
.Pa /dev/tty01
.El
.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 CAVEATS
When using a modular kernel (see
.Xr module 7 ) ,
the linux and linux32 emulations are not activated automatically (for
security reasons).
To activate the emulation, set the appropriate
.Xr sysctl 8 Ap s :
.Bd -literal
sysctl -w emul.linux.enabled=1
sysctl -w emul.linux32.enabled=1
.Ed
.Sh BUGS
The information about Linux distributions may become outdated.
.Pp
Absolute pathnames pointed to by symbolic links are only looked up in the
shadow root when the symbolic link itself was found by an absolute
pathname inside the shadow root.
This is not consistent.
.Pp
Linux executables cannot handle directory offset cookies > 32 bits.
Should such an offset occur, you will see the message
.Dq linux_getdents: dir offset too large for emulated program .
Currently, this can only
happen on NFS mounted file systems, 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
file system 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.