1.\" Copyright (c) 2000 Sheldon Hearn 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd May 6, 2021 28.Dt LINUX 4 29.Os 30.Sh NAME 31.Nm linux 32.Nd Linux ABI support 33.Sh SYNOPSIS 34To compile support for this ABI into an i386 kernel 35place the following line in your 36kernel configuration file: 37.Bd -ragged -offset indent 38.Cd "options COMPAT_LINUX" 39.Ed 40.Pp 41for an amd64 kernel use: 42.Bd -ragged -offset indent 43.Cd "options COMPAT_LINUX32" 44.Ed 45.Pp 46Alternatively, to load the ABI as a 47module at boot time, place the following line in 48.Xr loader.conf 5 : 49.Bd -literal -offset indent 50linux_load="YES" 51.Ed 52.Sh DESCRIPTION 53The 54.Nm 55module provides limited Linux ABI (application binary interface) compatibility, 56making it possible to run many unmodified Linux applications and libraries 57without the need for virtualization or emulation. 58Some of the facilities provided are: 59.Bl -bullet 60.It 61An image activator 62for correctly branded 63.Xr elf 5 64executable images 65.It 66Special signal handling for activated images 67.It 68Linux to native system call translation 69.It 70Linux-specific system calls 71.El 72.Pp 73Note that dynamically linked Linux executables 74will require a suitable environment in 75.Pa /compat/linux . 76This includes native Linux shared libraries, and Linux-specific virtual 77filesystems. 78To set it up, install the 79.Pa emulators/linux_base-c7 80port or the linux_base-c7 81package, and add the following line to the 82.Xr rc.conf 5 83file: 84.Pp 85.Dl linux_enable="YES" 86.Pp 87To avoid mounting Linux-specific filesystems at startup, also add the following 88line: 89.Pp 90.Dl linux_mounts_enable="NO" 91.Sh SYSCTL VARIABLES 92The following variables are available as both 93.Xr sysctl 8 94variables and 95.Xr loader 8 96tunables: 97.Bl -tag -width indent 98.It Va compat.linux.debug 99Enable debugging messages. 100Set to 0 to silence them. 101Defaults to 3. 102A setting of 1 prints debug messages, tells about unimplemented stuff (only 103once). 104Set to 2 is like 1, but also prints messages about implemented but not tested 105stuff (only once). 106Setting it to 3 or higher is like 2, but no rate limiting of messages. 107.It Va compat.linux.default_openfiles 108Default soft openfiles resource limit for Linux applications. 109Set to -1 to disable the limit. 110Defaults to 1024. 111.It Va compat.linux.emul_path 112Path to the Linux run-time environment. 113Defaults to 114.Pa /compat/linux . 115.It Va compat.linux.osname 116Linux kernel operating system name. 117.It Va compat.linux.osrelease 118Linux kernel operating system release. 119Changing this to something else is discouraged on non-development systems, 120because it may change the way Linux programs work. 121Recent versions of GNU libc are known to use different syscalls depending 122on the value of this sysctl. 123.It Va compat.linux.oss_version 124Linux Open Sound System version. 125.It Va compat.linux.preserve_vstatus 126When set to 1, it prevents Linux applications from resetting the 127.Xr termios 4 128VSTATUS setting. 129From a user perspective, this makes 130.Va SIGINFO 131work for Linux executables. 132Defaults to 0. 133.It Va compat.linux.setid_allowed 134Disable handling of set-user-ID and set-group-ID mode bits for the new 135process image file when image is to be executed under Linux ABI. 136When set, new Linux images always use credentials of the program 137that issued 138.Xr execve 2 139call, regardless of the image file mode. 140.Pp 141This might be reasonable or even required, because 142.Fx 143does not emulate Linux environment completely, and missed features 144could become holes. 145.El 146.Sh FILES 147.Bl -tag -width /compat/linux/dev/shm -compact 148.It Pa /compat/linux 149minimal Linux run-time environment 150.It Pa /compat/linux/dev 151device file system, see 152.Xr devfs 5 153.It Pa /compat/linux/dev/fd 154file descriptor file system mounted with the 155.Cm linrdlnk 156option, see 157.Xr fdescfs 5 158.It Pa /compat/linux/dev/shm 159in-memory file system, see 160.Xr tmpfs 5 161.It Pa /compat/linux/proc 162Linux process file system, see 163.Xr linprocfs 5 164.It Pa /compat/linux/sys 165Linux kernel objects file system, see 166.Xr linsysfs 5 167.El 168.Sh SEE ALSO 169.Xr brandelf 1 , 170.Xr pty 4 , 171.Xr elf 5 , 172.Xr fdescfs 5 , 173.Xr linprocfs 5 , 174.Xr linsysfs 5 , 175.Xr tmpfs 5 176.Sh HISTORY 177Linux ABI support first appeared in 178.Fx 2.1 . 179.Sh BUGS 180Support for some of the Linux-specific system calls and system call arguments 181is missing. 182