linux(4) Linux ABI support


To compile support for this ABI into an i386 kernel place the following line in your kernel configuration file:

for an amd64 kernel use:

options COMPAT_LINUX32

Alternatively, to load the ABI as a module at boot time, place the following line in loader.conf5:



The module provides limited Linux ABI (application binary interface) compatibility for userland applications. The module provides the following significant facilities:

  • An image activator for correctly branded elf(5) executable images
  • Special signal handling for activated images
  • Linux to native system call translation

It is important to note that the Linux ABI support it not provided through an emulator. Rather, a true (albeit limited) ABI implementation is provided.

The following sysctl(8) tunable variables are available:

Linux kernel operating system name.
Linux kernel operating system release. Changing this to something else is discouraged on non-development systems, because it may change the way Linux programs work. Recent versions of GNU libc are known to use different syscalls depending on the value of this sysctl.
Linux Open Sound System version.

The module can be linked into the kernel statically with the COMPAT_LINUX kernel configuration option or loaded as required. The following command will load the module if it is neither linked into the kernel nor already loaded as a module:

if ! kldstat -v | grep -E 'linux(aout|elf)' > /dev/null; then
        kldload linux > /dev/null 2>&1

Note that dynamically linked Linux executables will require a suitable environment in /compat/linux Specifically, the Linux run-time linker's hints files should be correctly initialized. For this reason, it is common to execute the following commands to prepare the system to correctly run Linux executables:

if [ -x /compat/linux/sbin/ldconfig ]; then
        /compat/linux/sbin/ldconfig -r /compat/linux

For information on loading the kernel loadable module automatically on system startup, see rc.conf5. This information applies regardless of whether the module is statically linked into the kernel or loaded as a module.


minimal Linux run-time environment
limited Linux process file system
limited Linux system file system


Linux ABI support first appeared in Fx 2.1 .