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

NAME
     compat_linux -- setup procedure for running Linux binaries

DESCRIPTION
     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
     used).

     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
     (respectively) 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
     runtime 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
     program 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
          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

          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 NetBSD system:
          /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)

          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.4.6.27
          /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
          install is:

          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
          version.  You can decide to replace the libc.so anyway, and that
          should leave you with:
          /emul/linux/lib/libc.so.4.6.29
          /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
          about that.

          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
          system (in the /emul/linux tree):
          /lib/ld.so
          /etc/ld.so.cache
          /etc/ld.so.config

     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
          version mismatches), and install them under /emul/linux (i.e.
          /foo/bar is installed as /emul/linux/foo/bar):

          /sbin/ldconfig
          /usr/bin/ldd
          /lib/libc.so.x.y.z
          /lib/ld.so

          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
          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:
          /usr/X11/lib
          /usr/local/lib

          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.
          Suppose that you have it installed as ldd-linux, it should produce
          something like:

                (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.
          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 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 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
     unexpectedly 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
     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:
           sunsite.unc.edu:/pub/Linux/distributions
           tsx-11.mit.edu:/pub/linux/distributions

     Some European mirrors:
           ftp.luth.se:/pub/linux/distributions
           ftp.demon.co.uk:/pub/linux/distributions
           src.doc.ic.ac.uk:/packages/linux/distributions

     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:

           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

     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:

           Package                 Location

           ldso                    diska2
           shlibs                  diska2
           oldlibs                 diskx6
           xf_lib                  diskx9

     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):
     slakware/a2/ldso.tgz
     slakware/a2/shlibs.tgz
     slakware/x6/oldlibs/tgz
     slakware/x9/xf_lib.tgz

     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.

   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,
     namely:
     /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.

BUGS
     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
     pathname 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
     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 -X option to mount_nfs(8).  The -2
     option to mount_nfs(8) will also have the desired effect, but is less
     preferable.

NetBSD 6.1.5                    April 30, 2007                    NetBSD 6.1.5