Linux binary compatibility is not turned on by default. The easiest way to enable this
functionality is to load the linux KLD object (“Kernel
LoaDable object”). You can load this module by typing the following as root:
#kldload linux
If you would like Linux compatibility to always be enabled, then you should add the
following line to /etc/rc.conf:
linux_enable="YES"
The kldstat(8) command can
be used to verify that the KLD is loaded:
%kldstat
Id Refs Address Size Name
1 2 0xc0100000 16bdb8 kernel
7 1 0xc24db000 d000 linux.ko
If for some reason you do not want to or cannot load the KLD, then you may statically
link Linux binary compatibility into the kernel by adding options
COMPAT_LINUX to your kernel configuration file. Then install your new kernel as
described in Chapter 8.
This is by far the easiest method to use when installing the runtime libraries. It is
just like installing any other port from the Ports Collection. Simply do the following:
You should now have working Linux binary compatibility. Some programs may complain
about incorrect minor versions of the system libraries. In general, however, this does
not seem to be a problem.
Note: There may be multiple versions of the emulators/linux_base port available, corresponding to different
versions of various Linux distributions. You should install the port most closely
resembling the requirements of the Linux applications you would like to install.
If you do not have the “ports” collection installed, 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, it will then
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.
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_base 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).
If you have access to a Linux system, see what shared libraries the application needs,
and copy them to your FreeBSD system. Look at the following example:
Let us assume you used FTP to get the Linux binary of Doom,
and put it on a Linux system you have access to. You then can check which shared
libraries it needs by running ldd linuxdoom, like so:
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:
Note: 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:
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 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:
Note: 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.
ELF binaries sometimes require an extra step of “branding”. If you attempt
to run an unbranded ELF binary, you will get an error message like the following:
%./my-linux-elf-binary
ELF binary type not known
Abort
To help the FreeBSD kernel distinguish between a FreeBSD ELF binary from a Linux
binary, use the brandelf(1)
utility.
%brandelf -t Linux my-linux-elf-binary
The GNU toolchain now places the appropriate branding information into ELF binaries
automatically, so this step should become increasingly unnecessary in the future.
resolv+: "bind" is an invalid keyword resolv+:
"hosts" is an invalid keyword
You will need to configure a /compat/linux/etc/host.conf
file containing:
order hosts, bind
multi on
The order here specifies that /etc/hosts is searched first
and DNS is searched second. When /compat/linux/etc/host.conf is
not installed, Linux applications find FreeBSD's /etc/host.conf
and complain about the incompatible FreeBSD syntax. You should remove bind if you have not configured a name server using the /etc/resolv.conf file.
