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35 .Nd Control POSIX shared memory segments
63 command manipulates the named POSIX shared memory segments.
64 It allows inspecting existing segments, dumping their metadata or contents,
67 Unlinking removes the name from the system and, when the last process
68 unmaps the segment and closes file descriptor pointing to the segment,
69 frees underlying memory.
71 The number of hard links as displayed by the
73 subcommand, is equal to the number of references to the underlying VM
75 It is almost always equal to the number of mappings +1, except
76 for transient references.
78 The following subcommands are provided:
79 .Bl -tag -width truncate
81 Create segments with the specified paths, if not exist.
84 optional numerical argument specifies initial access mode.
86 Unlink the paths specified.
88 List all linked named shared memory segments visible to the caller.
89 For each segment, the user and group owner, size, and path are displayed.
91 Output raw bytes values from the segment to standard output.
93 Print metadata for the specified path, in the format similar to the
97 Change the length of the segments.
100 option specifies new length.
101 The human-friendly 'k', 'm', 'g' suffixes can be used, see
102 .Xr expand_number 3 .
103 If the option is not specified, assumed length is zero.
106 For some commands, the following options may be provided:
109 If specified, requests human-readable display of size, see
110 .Xr humanize_number 3 .
112 Prevent translation of owner and group into symbolic names
113 using name-switch services, instead the raw numeric values are printed.
120 To show content of the shared memory segment with the path
123 .Dl "posixshmcontrol dump /q | hexdump -C"
125 To create a segment with the path
127 and then enlarge it to 1M, use the sequence of commands
128 .Dl "posixshmcontrol create /2"
129 .Dl "posixshmcontrol truncate -s 1m /2"
139 .Xr expand_number 3 ,
140 .Xr humanize_number 3 ,
150 command and this manual page were written by
151 .An Konstantin Belousov Aq Mt kib@freebsd.org
152 under sponsorship from The