.\" Copyright (c) 2000 Sheldon Hearn
.\" All rights reserved.
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.\" $FreeBSD$
.Dd August 17, 2000
.Dt LINUX 4 i386
.Os
.Sh NAME
.Nm linux
.Nd Linux ABI support
.Sh SYNOPSIS
To link Linux ABI support into the kernel:
.Cd "options COMPAT_LINUX"
.Pp
To load the Linux ABI support kernel module:
.Dl kldload linux
.Sh DESCRIPTION
The
.Nm
module provides limited
Linux ABI (application binary interface) compatibility
for userland applications.
The module provides the following significant facilities:
.Bl -bullet
.It
An image activator
for correctly branded
.Xr elf 5
executable images
.It
Special signal handling for activated images
.It
Linux to native system call translation
.El
.Pp
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.
.Pp
The following
.Xr sysctl 8
tunable variables are available:
.Bl -tag -width compat.linux.oss_version
.It compat.linux.osname
Linux kernel operating system name.
.It compat.linux.osrelease
Linux kernel operating system release.
.It compat.linux.oss_version
Linux Open Sound System version.
.El
.Pp
The
.Nm
module can be linked into the kernel statically with the
.Dv 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:
.Bd -literal -offset indent
if ! kldstat -v | grep -E 'linux(aout|elf)' > /dev/null; then
	kldload linux > /dev/null 2>&1
fi
.Ed
.Pp
Note that dynamically linked Linux executables
will require a suitable environment in
.Pa /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:
.Bd -literal -offset indent
if [ -x /compat/linux/sbin/ldconfig ]; then
	/compat/linux/sbin/ldconfig
fi
.Ed
.Pp
For information on loading the
.Nm
kernel loadable module automatically on system startup,
see
.Xr rc.conf 5 .
This information applies
regardless of whether the
.Nm
module is statically linked into the kernel
or loaded as a module.
.Sh FILES
.Bl -tag -width /compat/linux/proc -compact
.It Pa /compat/linux
minimal Linux run-time environment
.It Pa /compat/linux/proc
limited Linux process filesystem
.El
.Sh SEE ALSO
.Xr brandelf 1 ,
.Xr elf 5 ,
.Xr linprocfs 5
.Sh HISTORY
Linux ABI support first appeared in
.Fx 2.1 .