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				.\" Copyright (c) 2019 The FreeBSD Foundation, Inc.
				.\" All rights reserved.
				.\"
				.\" This documentation was written by
				.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
				.\" from the FreeBSD Foundation.
				.\"
				.\" Redistribution and use in source and binary forms, with or without
				.\" modification, are permitted provided that the following conditions
				.\" are met:
				.\" 1. Redistributions of source code must retain the above copyright
				.\" notice, this list of conditions and the following disclaimer.
				.\" 2. Redistributions in binary form must reproduce the above copyright
				.\" notice, this list of conditions and the following disclaimer in the
				.\" documentation and/or other materials provided with the distribution.
				.\"
				.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
				.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
				.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
				.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
				.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
				.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
				.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
				.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
				.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
				.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
				.\" SUCH DAMAGE.
				.\"
				.\" $FreeBSD$
				.\"
				.Dd May 27, 2019
				.Dt POSIXSHMCONTROL 1
				.Os
				.Sh NAME
				.Nm posixshmcontrol
				.Nd Control POSIX shared memory segments
				.Sh SYNOPSIS
				.Nm
				.Ar create
				.Op Fl m Ar mode
				.Op Pa path \&...
				.Nm
				.Ar rm
				.Op Pa path \&...
				.Nm
				.Ar ls
				.Op Fl h
				.Op Fl n
				.Nm
				.Ar dump
				.Op Pa path \&...
				.Nm
				.Ar stat
				.Op Fl h
				.Op Fl n
				.Op Pa path \&...
				.Nm
				.Ar truncate
				.Op Fl s Ar length
				.Op Pa path \&...
				.Sh DESCRIPTION
				The
				.Nm
				command manipulates the named POSIX shared memory segments.
				It allows inspecting existing segments, dumping their metadata or contents,
				and unlinking them.
				.Pp
				Unlinking removes the name from the system and, when the last process
				unmaps the segment and closes file descriptor pointing to the segment,
				frees underlying memory.
				.Pp
				The number of hard links as displayed by the
				.Ic stat
				subcommand, is equal to the number of references to the underlying VM
				object.
				It is almost always equal to the number of mappings +1, except
				for transient references.
				.Pp
				The following subcommands are provided:
				.Bl -tag -width truncate
				.It Ic create
				Create segments with the specified paths, if not exist.
				The
				.Ar mode
				optional numerical argument specifies initial access mode.
				.It Ic rm
				Unlink the paths specified.
				.It Ic ls
				List all linked named shared memory segments visible to the caller.
				For each segment, the user and group owner, size, and path are displayed.
				.It Ic dump
				Output raw bytes values from the segment to standard output.
				.It Ic stat
				Print metadata for the specified path, in the format similar to the
				.Xr stat 1
				utility.
				.It Ic truncate
				Change the length of the segments.
				Argument to the
				.Fl s
				option specifies new length, the human-friendly 'k', 'm', 'g' suffixes
				can be used, see
				.Xr expand_number 3.
				If the option is not specified, assumed length is zero.
				.El
				.Pp
				For some commands, the following options may be provided:
				.Bl -tag XX
				.It Fl h
				If specified, requests human-readable display of size, see
				.Xr humanize_number 3 .
				.It Fl n
				Prevent translation of owner and group into symbolic names
				using name-switch services, instead the raw numeric values are printed.
				.El
				.Sh EXIT STATUS
				.Ex -std
				.Sh EXAMPLES
				.Bl -bullet
				.It
				To show content of the shared memory segment with the path
				.Pa /1 ,
				use the command
				.Dl "posixshmcontrol dump /q \| hexdump -C"
				.It
				To create a segment with the path
				.Pa /2
				and then enlarge it to 1M, use the sequence of commands
				.Dl "posixshmcontrol create /2"
				.Dl "posixshmcontrol truncate -s 1m /2"
				.El
				.Sh SEE ALSO
				.Xr hexdump 1 ,
				.Xr stat 1 ,
				.Xr ftruncate 2 ,
				.Xr read 2 ,
				.Xr shm_open 2 ,
				.Xr shm_unlink 2 ,
				.Xr stat 2 ,
				.Xr expand_number 3 ,
				.Xr humanize_number 3 ,
				.Xr sysctl 3
				.Sh HISTORY
				The
				.Nm
				command appeared in
				.Fx 13.0 .
				.Sh AUTHORS
				The
				.Nm
				command and this manual page were written by
				.An Konstantin Belousov Aq Mt kib@freebsd.org
				under sponsorship from The FreeBSD Foundation.