MirBSD manpage: compat_linux(8)

COMPAT_LINUX(8)          BSD System Manager's Manual           COMPAT_LINUX(8)


     compat_linux - setup for running Linux binaries under emulation


     OpenBSD supports running Linux binaries. This only applies to i386 sys-
     tems for now. Both the a.out and ELF binary formats are supported. Most
     programs should work, including the ones that use the Linux SVGAlib. Ad-
     ditionally, OSS audio is emulated, so Linux binaries can access the na-
     tive 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. The default OS
     type is set to the host OS type, usually MirBSD, but can be changed via
     the kern.emul_uname sysctl.

     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 ex-
     ample, /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 con-
     figuration 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 suffi-
     cient 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

     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 per-
     form 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 run-
          ning `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 (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 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 -> /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 pro-
          gram should work fine with the slightly older version. libc.so can
          be replaced anyway, and that should leave:

                /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):


     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 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,
          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 ldconfig-linux and

          Create the file /emul/linux/etc/ld.so.conf, containing the direc-
          tories 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:


          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 it-
          self. 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 ex-
          tra library is needed. Which library this is, is shown in <major-
          name>, 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

     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 con-
     sisting 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 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 pack-
     ages needed from the following files (relative to the root of the
     Slackware distribution tree):


     Extract the files from these gzipped tarfiles in the /emul/linux directo-
     ry (possibly omitting or afterwards removing unnecessary files).

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
     /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

Programs using OSS (Linux) audio

     Only the DSP device is emulated, the following link should be created:

           /emul/linux/dev/dsp -> /dev/audio
     CD-ROM support requires a link to the CD-ROM device, similar to:

           /emul/linux/dev/cdrom -> /dev/cd0a (first CD-ROM)


     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.

MirBSD #10-current              March 2, 1995                                3

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