Most linux applications use shared libraries, so you are still not done until you install the shared libraries. It is possible to do this by hand, however, it is vastly simpler to just grab the linux_lib port:
% cd /usr/ports/emulators/linux_lib
% make all install
and you should have a working linux emulator. Legend (and the mail archives :-) seems to hold that Linux emulation works best with linux binaries linked against the ZMAGIC libraries; QMAGIC libraries (such as those used in Slackware V2.0) may tend to give the Linuxulator heartburn. Also, expect some programs to complain about incorrect minor versions of the system libraries. In general, however, this does not seem to be a problem.
If you do not have the ``ports'' distribution, you can install the libraries by hand instead. You will need the Linux shared libraries that the program depends on and the runtime linker. Also, you will need to create a "shadow root" directory, /compat/linux, for Linux libraries on your FreeBSD system. Any shared libraries opened by Linux programs run under FreeBSD will look in this tree first. So, if a Linux program loads, for example, /lib/libc.so, FreeBSD will first try to open /compat/linux/lib/libc.so, and if that does not exist then it will try /lib/libc.so. Shared libraries should be installed in the shadow tree /compat/linux/lib rather than the paths that the Linux ld.so reports.
FreeBSD 2.2-RELEASE and later works slightly differently with respect to /compat/linux: all files, not just libraries, are searched for from the ``shadow root'' /compat/linux.
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 FreeBSD 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.
What if you install the linux_lib port and your application still complains about missing shared libraries? How do you 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 FreeBSD system to do the necessary installation steps).
If you have access to a Linux system, see what shared libraries the application needs, and copy them to your FreeBSD 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':
% 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 to get all the files from the last column, and put them under /compat/linux, with the names in the first column as symbolic links pointing to them. This means you eventually have these files on your FreeBSD system:
/compat/linux/usr/X11/lib/libXt.so.3.1.0
/compat/linux/usr/X11/lib/libXt.so.3 -> libXt.so.3.1.0
/compat/linux/usr/X11/lib/libX11.so.3.1.0
/compat/linux/usr/X11/lib/libX11.so.3 -> libX11.so.3.1.0
/compat/linux/lib/libc.so.4.6.29
/compat/linux/lib/libc.so.4 -> libc.so.4.6.29
Note that if you already have a Linux shared library with a matching major revision number to the first column of the 'ldd' output, you will not 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:
/compat/linux/lib/libc.so.4.6.27
/compat/linux/lib/libc.so.4 -> libc.so.4.6.27
and you find a new binary that claims to require a later version according to the output of ldd:
libc.so.4 (DLL Jump 4.5pl26) -> libc.so.4.6.29
If it is only one or two versions out of date in the in the trailing digit then do not worry about copying /lib/libc.so.4.6.29 too, because the program should work fine with the slightly older version. However, if you like you can decide to replace the libc.so anyway, and that should leave you with:
/compat/linux/lib/libc.so.4.6.29
/compat/linux/lib/libc.so.4 -> libc.so.4.6.29
Please note that the symbolic link mechanism is only needed for Linux binaries. The FreeBSD runtime linker takes care of looking for matching major revision numbers itself and you do not need to worry about it.
This section applies only to FreeBSD 2.2-RELEASE and later. Those running 2.1-STABLE should skip this section.
Finally, if you run FreeBSD 2.2-RELEASE 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 FreeBSD system (to the /compat/linux tree):
/compat/linux/lib/ld.so
/compat/linux/etc/ld.so.config
If you do not have access to a Linux system, 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 us assume you know where to get the files.
Retrieve the following files (all from the same ftp site to avoid any version mismatches), and install them under /compat/linux (i.e. /foo/bar is installed as /compat/linux/foo/bar):
/sbin/ldconfig
/usr/bin/ldd
/lib/libc.so.x.y.z
/lib/ld.so
ldconfig and ldd do not necessarily need to be under /compat/linux; you can install them elsewhere in the system too. Just make sure they do not conflict with their FreeBSD counterparts. A good idea would be to install them in /usr/local/bin as ldconfig-linux and ldd-linux.
Create the file /compat/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
When a linux binary opens a library such as /lib/libc.so the emulator maps the name to /compat/linux/lib/libc.so internally. All linux libraries should be installed under /compat/linux (e.g. /compat/linux/lib/libc.so, /compat/linux/usr/X11/lib/libX11.so, etc.) in order for the emulator to find them.
Those running FreeBSD 2.2-RELEASE should run the Linux ldconfig program.
% cd /compat/linux/lib
% /compat/linux/sbin/ldconfig
Ldconfig is statically linked, so it does not need any shared libraries to run. It creates the file /compat/linux/etc/ld.so.cache which contains the names of all the shared libraries and should be rerun to recreate this file whenever you install additional shared libraries.
On 2.1-STABLE do not install /compat/linux/etc/ld.so.cache or run ldconfig; in 2.1-STABLE the syscalls are implemented differently and ldconfig is not needed or used.
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. Supposing that you have it 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, 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 /compat/linux tree. To do this, you 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 you need an extra library. The library needed is shown in majorname and 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.