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COMPAT_LINUX(8) NetBSD System Manager's Manual COMPAT_LINUX(8)
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compat_linux -- setup procedure for running Linux binaries
NetBSD 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). NetBSD 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
The Linux compatibility feature is active for kernels compiled with the
COMPAT_LINUX option enabled. If support for Linux a.out executables is
desired, the EXEC_AOUT option should be enabled in addition to option
COMPAT_LINUX. Similarly, if support for Linux 32-bit and/or 64-bit ELF
executables is desired, the EXEC_ELF32 and/or EXEC_ELF64 options (respec-
tively) should be enabled in addition to COMPAT_LINUX.
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 run-
time linker. Also, you will need to create a ``shadow root'' directory
for Linux binaries on your NetBSD system. This directory is named
/emul/linux or /emul/linux32 for 32bit emulation on 64bit systems. Any
file operations done by Linux programs run under NetBSD will look in this
directory first. So, if a Linux program opens, for example, /etc/passwd,
NetBSD 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 NetBSD counterparts.
Shared libraries should also be installed in the shadow tree. Filenames
that start "/../" are only looked up in the real root.
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 pro-
gram on your NetBSD 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.
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 NetBSD system to do the
necessary installation steps).
1. For i386, you can simply install the SuSE shared libs using the
pkgsrc/emulators/suse100_linux package(s). On PowerPC ports, the
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.
2. 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 NetBSD 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
(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
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 sym-
bolic links pointing to them. This means you eventually have these
files on your NetBSD system:
/emul/linux/usr/X11/lib/libXt.so.3 (symbolic link to the above)
/emul/linux/usr/X11/lib/libX11.so.3 (symbolic link to the above)
/emul/linux/lib/libc.so.4 (symbolic link to the above)
Note that if you already have a Linux shared library with a matching
major revision number to the first column of the 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:
/emul/linux/lib/libc.so.4 -> /emul/linux/lib/libc.so.4.6.27
and you find that the ldd output for a new binary you want to
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
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 ver-
sion. You can decide to replace the libc.so anyway, and that should
leave you with:
/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 NetBSD runtime linker takes care of looking for
matching major revision numbers itself, you don't need to worry
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 NetBSD sys-
tem (in the /emul/linux tree):
3. 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.
Retrieve the following files (from _one_ ftp site to avoid any ver-
sion mismatches), and install them under /emul/linux (i.e. /foo/bar
is installed as /emul/linux/foo/bar):
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 NetBSD 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 directo-
ries 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:
Note that these are mapped to /emul/linux/XXXX by NetBSD'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 ldconfig each time you add a new shared library.
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. Sup-
pose that you have it installed as ldd-linux, it should produce
(me@netbsd) ldd-linux `which ldd-linux`
libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29
This being done, you are ready to install new Linux binaries. When-
ever 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 ldd on the new pro-
gram, 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 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.
4. Set up linux specific devices:
(me@netbsd) cd /usr/share/examples/emul/linux/etc
(me@netbsd) cp LINUX_MAKEDEV /emul/linux/dev
(me@netbsd) cd /emul/linux/dev && sh LINUX_MAKEDEV all
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 unexpect-
edly or even crash.
Mount procfs on NetBSD using following command:
(me@netbsd) mount_procfs -o linux procfs /emul/linux/proc
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 /etc/fstab.
procfs /emul/linux/proc procfs ro,linux
See mount_procfs(8) for further information.
Setting up other files
Newer version of Linux use /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 /emul/linux/etc.
Finding the necessary files
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.
Linux is distributed by several groups that make their own set of bina-
ries 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:
Some European mirrors:
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 con-
tents 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:
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:
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
Extract the files from these gzipped tarfiles in your /emul/linux direc-
tory (possibly omitting or afterwards removing files you don't need), and
you are done.
Programs using SVGAlib
SVGAlib binaries require some extra care. You need to have options
WSDISPLAY_COMPAT_USL in your kernel (see wscons(4)), and you will also
have to create some symbolic links in the /emul/linux/dev directory,
/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
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.
When using a modular kernel (see module(7)), the linux and linux32 emula-
tions are not activated automatically (for security reasons). To acti-
vate the emulation, set the appropriate sysctl(8)'s:
sysctl -w emul.linux.enabled=1
sysctl -w emul.linux32.enabled=1
The information about Linux distributions may become outdated.
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 path-
name inside the shadow root. This is not consistent.
Linux executables cannot 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 file systems, mounted from servers that return off-
sets 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 -X option to mount_nfs(8). The -2 option
to mount_nfs(8) will also have the desired effect, but is less prefer-
NetBSD 9.99 September 29, 2017 NetBSD 9.99
Modified for NetBSD
by Kimmo Suominen