LINUX(4)               FreeBSD Kernel Interfaces Manual               LINUX(4)

NAME
     linux - Linux ABI support

SYNOPSIS
     To enable the Linux ABI at boot time, place the following line in
     rc.conf(5):

           linux_enable="YES"

DESCRIPTION
     The linux kernel module provides limited Linux ABI (application binary
     interface) compatibility, making it possible to run many unmodified Linux
     applications without the need for virtualization or emulation.  Some of
     the facilities provided are:

     •   Linux to native system call translation

     •   Linux-specific system calls

     •   Special signal handling for Linux processes

     •   Path translation mechanism

     •   Linux-specific virtual file systems

     The path translation mechanism makes Linux processes look up file paths
     under emul_path (defaulting to /compat/linux) before /.  For example,
     when Linux process attempts to open /etc/passwd, it will really access
     /compat/linux/etc/passwd, unless the latter does not exist.  This is used
     to make sure Linux processes load Linux shared libraries instead of their
     similarly-named FreeBSD counterparts, and also to provide alternative
     versions of certain other files and virtual file systems.

     To install Linux shared libraries and system files into /compat/linux,
     either use the emulators/linux_base-c7 port or package, or debootstrap(8)
     installed from sysutils/debootstrap.

     To avoid mounting Linux-specific filesystems at startup, add the
     following line to the rc.conf(5) file:

           linux_mounts_enable="NO"

SYSCTL VARIABLES
     The following variables are available as both sysctl(8) variables and
     loader(8) tunables:

     compat.linux.debug
             Enable debugging messages.  Set to 0 to silence them.  Defaults
             to 3.  A setting of 1 prints debug messages, tells about
             unimplemented stuff (only once).  Set to 2 is like 1, but also
             prints messages about implemented but not tested stuff (only
             once).  Setting it to 3 or higher is like 2, but no rate limiting
             of messages.

     compat.linux.default_openfiles
             Default soft openfiles resource limit for Linux applications.
             Set to -1 to disable the limit.  Defaults to 1024.

     compat.linux.emul_path
             Path to the Linux run-time environment.  Defaults to
             /compat/linux.

     compat.linux.osname
             Linux kernel operating system name.  Defaults to "Linux".

     compat.linux.osrelease
             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.  Some versions of GNU
             libc are known to use different syscalls depending on the value
             of this sysctl.

     compat.linux.oss_version
             Linux Open Sound System version.  Defaults to 198144.

     compat.linux.preserve_vstatus
             When set to 1, it prevents Linux applications from resetting the
             termios(4) VSTATUS setting.  From a user perspective, this makes
             SIGINFO work for Linux executables.  Defaults to 1.

     compat.linux.setid_allowed
             Enable handling of set-user-ID and set-group-ID mode bits for the
             new process image file when image is to be executed under Linux
             ABI.  When set to 0, new Linux images always use credentials of
             the program that issued the execve(2) call, regardless of the
             image file mode.  This might be reasonable or even required,
             because FreeBSD does not emulate the Linux environment
             completely, and missed features may result in security
             vulnerabilities.  Defaults to 1.

FILES
     /compat/linux          Linux run-time environment
     /compat/linux/dev      device file system, see devfs(5)
     /compat/linux/dev/fd   file descriptor file system mounted with the
                            linrdlnk option, see fdescfs(5)
     /compat/linux/dev/shm  in-memory file system, see tmpfs(5)
     /compat/linux/proc     Linux process file system, see linprocfs(5)
     /compat/linux/sys      Linux kernel objects file system, see linsysfs(5)

SEE ALSO
     brandelf(1), pty(4), elf(5), fdescfs(5), linprocfs(5), linsysfs(5),
     tmpfs(5)

HISTORY
     Linux ABI support first appeared for i386 in FreeBSD 2.1.  Support for
     amd64 binaries first appeared in FreeBSD 10.3.  Support for arm64
     binaries first appeared in FreeBSD 12.0.

BUGS
     Support for some of the Linux-specific system calls and system call
     arguments is missing.

FreeBSD 13.1-RELEASE-p6         January 9, 2022        FreeBSD 13.1-RELEASE-p6