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