b896bdb86d
From a user point of view, this makes ^T work out of the box. Reviewed By: debdrup (man page) Sponsored By: EPSRC Differential Revision: https://reviews.freebsd.org/D33842
189 lines
5.6 KiB
Groff
189 lines
5.6 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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.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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