1.\" Copyright (c) 2019 The FreeBSD Foundation, Inc. 2.\" 3.\" This documentation was written by 4.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship 5.\" from the FreeBSD Foundation. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" $FreeBSD$ 29.\" 30.Dd February 26, 2022 31.Dt POSIXSHMCONTROL 1 32.Os 33.Sh NAME 34.Nm posixshmcontrol 35.Nd Control POSIX shared memory segments 36.Sh SYNOPSIS 37.Nm 38.Ar create 39.Op Fl m Ar mode 40.Op Pa path \&... 41.Nm 42.Ar rm 43.Op Pa path \&... 44.Nm 45.Ar ls 46.Op Fl h 47.Op Fl n 48.Op Fl j Ar jail 49.Nm 50.Ar dump 51.Op Pa path \&... 52.Nm 53.Ar stat 54.Op Fl h 55.Op Fl n 56.Op Pa path \&... 57.Nm 58.Ar truncate 59.Op Fl s Ar length 60.Op Pa path \&... 61.Sh DESCRIPTION 62The 63.Nm 64command manipulates the named POSIX shared memory segments. 65It allows inspecting existing segments, dumping their metadata or contents, 66and unlinking them. 67.Pp 68Unlinking removes the name from the system and, when the last process 69unmaps the segment and closes file descriptor pointing to the segment, 70frees underlying memory. 71.Pp 72The number of hard links as displayed by the 73.Ic stat 74subcommand, is equal to the number of references to the underlying VM 75object. 76It is almost always equal to the number of mappings +1, except 77for transient references. 78.Pp 79The following subcommands are provided: 80.Bl -tag -width truncate 81.It Ic create 82Create segments with the specified paths, if not exist. 83The 84.Ar mode 85optional numerical argument specifies initial access mode. 86.It Ic rm 87Unlink the paths specified. 88.It Ic ls 89List all linked named shared memory segments visible to the caller. 90For each segment, the user and group owner, size, and path are displayed. 91The 92.Fl j 93option limits the output to segments within the specified 94.Ar jail 95name or id. 96.It Ic dump 97Output raw bytes values from the segment to standard output. 98.It Ic stat 99Print metadata for the specified path, in the format similar to the 100.Xr stat 1 101utility. 102.It Ic truncate 103Change the length of the segments. 104Argument to the 105.Fl s 106option specifies new length. 107The human-friendly 'k', 'm', 'g' suffixes can be used, see 108.Xr expand_number 3 . 109If the option is not specified, assumed length is zero. 110.El 111.Pp 112For some commands, the following options may be provided: 113.Bl -tag -width XXX 114.It Fl h 115If specified, requests human-readable display of size, see 116.Xr humanize_number 3 . 117.It Fl n 118Prevent translation of owner and group into symbolic names 119using name-switch services, instead the raw numeric values are printed. 120.El 121.Sh EXIT STATUS 122.Ex -std 123.Sh EXAMPLES 124.Bl -bullet 125.It 126To show content of the shared memory segment with the path 127.Pa /1 , 128use the command 129.Dl "posixshmcontrol dump /1 | hexdump -C" 130.It 131To create a segment with the path 132.Pa /2 133and then enlarge it to 1M, use the sequence of commands 134.Dl "posixshmcontrol create /2" 135.Dl "posixshmcontrol truncate -s 1m /2" 136.El 137.Sh SEE ALSO 138.Xr hexdump 1 , 139.Xr stat 1 , 140.Xr ftruncate 2 , 141.Xr read 2 , 142.Xr shm_open 2 , 143.Xr shm_unlink 2 , 144.Xr stat 2 , 145.Xr expand_number 3 , 146.Xr humanize_number 3 , 147.Xr sysctl 3 148.Sh HISTORY 149The 150.Nm 151command appeared in 152.Fx 12.1 . 153.Sh AUTHORS 154The 155.Nm 156command and this manual page were written by 157.An Konstantin Belousov Aq Mt kib@freebsd.org 158under sponsorship from The 159.Fx 160Foundation. 161