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COMPAT_LINUX(8)		  BSD 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 (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
	  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 sym‐
	  bolic links pointing to them.	 This means you eventually have these
	  files on your NetBSD system:
	  /emul/linux/usr/X11/lib/libXt.so.3.1.0
	  /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 ver‐
	  sion.	 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 sys‐
	  tem (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 ver‐
	  sion 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 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:
	  /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.	Sup‐
	  pose 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.	 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 indi‐
     vidual 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 subdirec‐
     tory, 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 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,
     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 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‐
     able.

BSD				April 30, 2007				   BSD
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