d5dc757e84
Historically 32-bit Linuxulator under amd64 emulated the real i386
behavior. Since 3d8dd983 the old i386 Linux world can't be used under
amd64 Linuxulator as it don't know anything about amd64 machine (which
is returned now by newuname() syscall). So, add a knob to allow to swith
the behavior and use i386 Linux binaries on amd64.
Set knob to the new behavior as I think this is common to the modern
Linux distros.
Reviewed by: Pau Amma (doc), emaste
Differential revision: https://reviews.freebsd.org/D34708
MFC after: 2 weeks
195 lines
5.9 KiB
Groff
195 lines
5.9 KiB
Groff
.\" Copyright (c) 2000 Sheldon Hearn
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 9, 2022
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.Dt LINUX 4
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.Os
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.Sh NAME
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.Nm linux
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.Nd Linux ABI support
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.Sh SYNOPSIS
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To enable the Linux ABI at boot time, place the following line in
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.Xr rc.conf 5 :
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.Bd -literal -offset indent
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linux_enable="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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kernel module provides limited Linux ABI (application binary interface)
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compatibility, making it possible to run many unmodified Linux applications
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without the need for virtualization or emulation.
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Some of the facilities provided are:
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.Bl -bullet
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.It
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Linux to native system call translation
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.It
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Linux-specific system calls
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.It
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Special signal handling for Linux processes
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.It
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Path translation mechanism
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.It
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Linux-specific virtual file systems
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.El
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.Pp
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The path translation mechanism makes Linux processes look up file paths
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under
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.Va emul_path
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(defaulting to
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.Pa /compat/linux )
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before
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.Pa / .
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For example, when Linux process attempts to open
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.Pa /etc/passwd ,
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it will really access
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.Pa /compat/linux/etc/passwd ,
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unless the latter does not exist.
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This is used to make sure Linux processes load Linux shared libraries
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instead of their similarly-named FreeBSD counterparts, and also
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to provide alternative versions of certain other files and virtual
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file systems.
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.Pp
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To install Linux shared libraries and system files into
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.Pa /compat/linux ,
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either use the
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.Pa emulators/linux_base-c7
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port or package,
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or
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.Xr debootstrap 8
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installed from
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.Pa sysutils/debootstrap .
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.Pp
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To avoid mounting Linux-specific filesystems at startup, add the following
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line to the
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.Xr rc.conf 5
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file:
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.Pp
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.Dl linux_mounts_enable="NO"
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.Sh SYSCTL VARIABLES
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The following variables are available as both
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.Xr sysctl 8
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variables and
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.Xr loader 8
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tunables:
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.Bl -tag -width indent
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.It Va compat.linux.debug
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Enable debugging messages.
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Set to 0 to silence them.
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Defaults to 3.
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A setting of 1 prints debug messages, tells about unimplemented stuff (only
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once).
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Set to 2 is like 1, but also prints messages about implemented but not tested
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stuff (only once).
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Setting it to 3 or higher is like 2, but no rate limiting of messages.
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.It Va compat.linux.default_openfiles
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Default soft openfiles resource limit for Linux applications.
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Set to -1 to disable the limit.
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Defaults to 1024.
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.It Va compat.linux.emul_path
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Path to the Linux run-time environment.
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Defaults to
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.Pa /compat/linux .
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.It Va compat.linux.osname
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Linux kernel operating system name.
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Defaults to "Linux".
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.It Va compat.linux.osrelease
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Linux kernel operating system release.
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Changing this to something else is discouraged on non-development systems,
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because it may change the way Linux programs work.
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Some versions of GNU libc are known to use different syscalls depending
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on the value of this sysctl.
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.It Va compat.linux.oss_version
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Linux Open Sound System version.
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Defaults to 198144.
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.It Va compat.linux.preserve_vstatus
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When set to 1, it prevents Linux applications from resetting the
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.Xr termios 4
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VSTATUS setting.
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From a user perspective, this makes
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.Va SIGINFO
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work for Linux executables.
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Defaults to 1.
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.It Va compat.linux.setid_allowed
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Enable handling of set-user-ID and set-group-ID mode bits for the new
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process image file when image is to be executed under Linux ABI.
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When set to 0, new Linux images always use credentials of the program
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that issued the
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.Xr execve 2
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call, regardless of the image file mode.
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This might be reasonable or even required, because
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.Fx
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does not emulate the Linux environment completely, and missed features
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may result in security vulnerabilities.
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Defaults to 1.
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.It Va compat.linux32.emulate_i386
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In the x86_64 (amd64) world enable the real i386 Linuxulator behavior.
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For example, when set to 0, Linux uname -m will return "x86_64" even if
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uname itself is a i386 Linux executable. When set to 1, Linux i386
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uname -m will return "i686".
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Defaults to 0.
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.El
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.Sh FILES
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.Bl -tag -width /compat/linux/dev/shm -compact
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.It Pa /compat/linux
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Linux run-time environment
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.It Pa /compat/linux/dev
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device file system, see
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.Xr devfs 5
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.It Pa /compat/linux/dev/fd
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file descriptor file system mounted with the
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.Cm linrdlnk
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option, see
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.Xr fdescfs 5
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.It Pa /compat/linux/dev/shm
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in-memory file system, see
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.Xr tmpfs 5
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.It Pa /compat/linux/proc
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Linux process file system, see
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.Xr linprocfs 5
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.It Pa /compat/linux/sys
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Linux kernel objects file system, see
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.Xr linsysfs 5
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.El
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.Sh SEE ALSO
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.Xr brandelf 1 ,
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.Xr pty 4 ,
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.Xr elf 5 ,
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.Xr fdescfs 5 ,
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.Xr linprocfs 5 ,
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.Xr linsysfs 5 ,
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.Xr tmpfs 5
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.Sh HISTORY
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Linux ABI support first appeared for i386 in
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.Fx 2.1 .
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Support for amd64 binaries first appeared in
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.Fx 10.3 .
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Support for arm64 binaries first appeared in
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.Fx 12.0 .
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.Sh BUGS
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Support for some of the Linux-specific system calls and system call arguments
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is missing.
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