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).
- 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.
- 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
- 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.
- 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.
CAVEATS
When using a modular kernel (see
module(7)), the linux and
linux32 emulations are not activated automatically (for security reasons). To
activate the emulation, set the appropriate
sysctl(8)'s:
sysctl -w emul.linux.enabled=1
sysctl -w emul.linux32.enabled=1
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.