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.Dd January 9, 2022 26.Dt LINUX 4 27.Os 28.Sh NAME 29.Nm linux 30.Nd Linux ABI support 31.Sh SYNOPSIS 32To enable the Linux ABI at boot time, place the following line in 33.Xr rc.conf 5 : 34.Bd -literal -offset indent 35linux_enable="YES" 36.Ed 37.Sh DESCRIPTION 38The 39.Nm 40kernel module provides limited Linux ABI (application binary interface) 41compatibility, making it possible to run many unmodified Linux applications 42without the need for virtualization or emulation. 43Some of the facilities provided are: 44.Bl -bullet 45.It 46Linux to native system call translation 47.It 48Linux-specific system calls 49.It 50Special signal handling for Linux processes 51.It 52Path translation mechanism 53.It 54Linux-specific virtual file systems 55.El 56.Pp 57The path translation mechanism makes Linux processes look up file paths 58under 59.Va emul_path 60(defaulting to 61.Pa /compat/linux ) 62before 63.Pa / . 64For example, when Linux process attempts to open 65.Pa /etc/passwd , 66it will really access 67.Pa /compat/linux/etc/passwd , 68unless the latter does not exist. 69This is used to make sure Linux processes load Linux shared libraries 70instead of their similarly-named FreeBSD counterparts, and also 71to provide alternative versions of certain other files and virtual 72file systems. 73.Pp 74To install Linux shared libraries and system files into 75.Pa /compat/linux , 76either use the 77.Pa emulators/linux_base-c7 78port or package, 79or 80.Xr debootstrap 8 81installed from 82.Pa sysutils/debootstrap . 83.Pp 84To avoid mounting Linux-specific filesystems at startup, add the following 85line to the 86.Xr rc.conf 5 87file: 88.Pp 89.Dl linux_mounts_enable="NO" 90.Sh SYSCTL VARIABLES 91The following variables are available as both 92.Xr sysctl 8 93variables and 94.Xr loader 8 95tunables: 96.Bl -tag -width indent 97.It Va compat.linux.debug 98Enable debugging messages. 99Set to 0 to silence them. 100Defaults to 3. 101A setting of 1 prints debug messages, tells about unimplemented stuff (only 102once). 103Set to 2 is like 1, but also prints messages about implemented but not tested 104stuff (only once). 105Setting it to 3 or higher is like 2, but no rate limiting of messages. 106.It Va compat.linux.default_openfiles 107Default soft openfiles resource limit for Linux applications. 108Set to -1 to disable the limit. 109Defaults to 1024. 110.It Va compat.linux.emul_path 111Path to the Linux run-time environment. 112Defaults to 113.Pa /compat/linux . 114.It Va compat.linux.osname 115Linux kernel operating system name. 116Defaults to "Linux". 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. 121Some 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. 125Defaults to 198144. 126.It Va compat.linux.preserve_vstatus 127When set to 1, it prevents Linux applications from resetting the 128.Xr termios 4 129VSTATUS setting. 130From a user perspective, this makes 131.Va SIGINFO 132work for Linux executables. 133Defaults to 1. 134.It Va compat.linux.setid_allowed 135Enable handling of set-user-ID and set-group-ID mode bits for the new 136process image file when image is to be executed under Linux ABI. 137When set to 0, new Linux images always use credentials of the program 138that issued the 139.Xr execve 2 140call, regardless of the image file mode. 141This might be reasonable or even required, because 142.Fx 143does not emulate the Linux environment completely, and missed features 144may result in security vulnerabilities. 145Defaults to 1. 146.It Va compat.linux32.emulate_i386 147In the x86_64 (amd64) world enable the real i386 Linuxulator behavior. 148For example, when set to 0, Linux uname -m will return "x86_64" even if 149uname itself is a i386 Linux executable. When set to 1, Linux i386 150uname -m will return "i686". 151Defaults to 0. 152.El 153.Sh FILES 154.Bl -tag -width /compat/linux/dev/shm -compact 155.It Pa /compat/linux 156Linux run-time environment 157.It Pa /compat/linux/dev 158device file system, see 159.Xr devfs 5 160.It Pa /compat/linux/dev/fd 161file descriptor file system mounted with the 162.Cm linrdlnk 163option, see 164.Xr fdescfs 5 165.It Pa /compat/linux/dev/shm 166in-memory file system, see 167.Xr tmpfs 5 168.It Pa /compat/linux/proc 169Linux process file system, see 170.Xr linprocfs 5 171.It Pa /compat/linux/sys 172Linux kernel objects file system, see 173.Xr linsysfs 5 174.El 175.Sh SEE ALSO 176.Xr brandelf 1 , 177.Xr pty 4 , 178.Xr elf 5 , 179.Xr fdescfs 5 , 180.Xr linprocfs 5 , 181.Xr linsysfs 5 , 182.Xr tmpfs 5 183.Sh HISTORY 184Linux ABI support first appeared for i386 in 185.Fx 2.1 . 186Support for amd64 binaries first appeared in 187.Fx 10.3 . 188Support for arm64 binaries first appeared in 189.Fx 12.0 . 190.Sh BUGS 191Support for some of the Linux-specific system calls and system call arguments 192is missing. 193