xref: /freebsd/usr.bin/posixshmcontrol/posixshmcontrol.1 (revision 9f23cbd6cae82fd77edfad7173432fa8dccd0a95)
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3.\" This documentation was written by
4.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
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28.\" $FreeBSD$
29.\"
30.Dd May 25, 2023
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 l Ar pagesize
40.Op Fl m Ar mode
41.Op Pa path \&...
42.Nm
43.Ar rm
44.Op Pa path \&...
45.Nm
46.Ar ls
47.Op Fl h
48.Op Fl n
49.Op Fl j Ar jail
50.Nm
51.Ar dump
52.Op Pa path \&...
53.Nm
54.Ar stat
55.Op Fl h
56.Op Fl n
57.Op Pa path \&...
58.Nm
59.Ar truncate
60.Op Fl s Ar length
61.Op Pa path \&...
62.Sh DESCRIPTION
63The
64.Nm
65command manipulates the named POSIX shared memory segments.
66It allows inspecting existing segments, dumping their metadata or contents,
67and unlinking them.
68.Pp
69Unlinking removes the name from the system and, when the last process
70unmaps the segment and closes file descriptor pointing to the segment,
71frees underlying memory.
72.Pp
73The number of hard links as displayed by the
74.Ic stat
75subcommand, is equal to the number of references to the underlying VM
76object.
77It is almost always equal to the number of mappings +1, except
78for transient references.
79.Pp
80The following subcommands are provided:
81.Bl -tag -width truncate
82.It Ic create
83Create segments with the specified paths, if they do not already exist.
84.Pp
85The optional
86.Ar pagesize
87argument specifies the size of the virtual pages used to map the
88object with
89.Xr mmap 2 .
90By default, the system page size is used, but on some platforms a
91larger page size can be specified.
92The size of an object backed by large pages must be a multiple of the
93specified page size.
94The
95.Va hw.pagesizes
96sysctl variable lists the available page sizes.
97.Pp
98The optional numerical
99.Ar mode
100argument specifies the initial access mode.
101.It Ic rm
102Unlink the paths specified.
103.It Ic ls
104List all linked named shared memory segments visible to the caller.
105For each segment, the user and group owner, size, and path are displayed.
106The
107.Fl j
108option limits the output to segments within the specified
109.Ar jail
110name or id.
111.It Ic dump
112Output raw bytes values from the segment to standard output.
113.It Ic stat
114Print metadata for the specified path, in the format similar to the
115.Xr stat 1
116utility.
117.It Ic truncate
118Change the length of the segments.
119Argument to the
120.Fl s
121option specifies new length.
122The human-friendly 'k', 'm', 'g' suffixes can be used, see
123.Xr expand_number 3 .
124If the option is not specified, assumed length is zero.
125.El
126.Pp
127For some commands, the following options may be provided:
128.Bl -tag -width XXX
129.It Fl h
130If specified, requests human-readable display of size, see
131.Xr humanize_number 3 .
132.It Fl n
133Prevent translation of owner and group into symbolic names
134using name-switch services, instead the raw numeric values are printed.
135.El
136.Sh EXIT STATUS
137.Ex -std
138.Sh EXAMPLES
139.Bl -bullet
140.It
141To show content of the shared memory segment with the path
142.Pa /1 ,
143use the command
144.Dl "posixshmcontrol dump /1 | hexdump -C"
145.It
146To create a segment with the path
147.Pa /2
148and then enlarge it to 1M, use the sequence of commands
149.Dl "posixshmcontrol create /2"
150.Dl "posixshmcontrol truncate -s 1m /2"
151.El
152.Sh SEE ALSO
153.Xr hexdump 1 ,
154.Xr stat 1 ,
155.Xr ftruncate 2 ,
156.Xr mmap 2 ,
157.Xr read 2 ,
158.Xr shm_open 2 ,
159.Xr shm_unlink 2 ,
160.Xr stat 2 ,
161.Xr expand_number 3 ,
162.Xr humanize_number 3 ,
163.Xr shm_create_largepage 3 ,
164.Xr sysctl 3
165.Sh HISTORY
166The
167.Nm
168command appeared in
169.Fx 12.1 .
170.Sh AUTHORS
171The
172.Nm
173command and this manual page were written by
174.An Konstantin Belousov Aq Mt kib@freebsd.org
175under sponsorship from The
176.Fx
177Foundation.
178