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POSIXSHMCONTROL(1) FreeBSD General Commands Manual POSIXSHMCONTROL(1) NAME posixshmcontrol -- Control POSIX shared memory segments SYNOPSIS posixshmcontrol create [-m mode] [path ...] posixshmcontrol rm [path ...] posixshmcontrol ls [-h] [-n] posixshmcontrol dump [path ...] posixshmcontrol stat [-h] [-n] [path ...] posixshmcontrol truncate [-s length] [path ...] DESCRIPTION The posixshmcontrol command manipulates the named POSIX shared memory segments. It allows inspecting existing segments, dumping their metadata or contents, and unlinking them. Unlinking removes the name from the system and, when the last process un- maps the segment and closes file descriptor pointing to the segment, frees underlying memory. The number of hard links as displayed by the stat subcommand, is equal to the number of references to the underlying VM object. It is almost al- ways equal to the number of mappings +1, except for transient references. The following subcommands are provided: create Create segments with the specified paths, if not exist. The mode optional numerical argument specifies initial access mode. rm Unlink the paths specified. 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. dump Output raw bytes values from the segment to standard output. stat Print metadata for the specified path, in the format similar to the stat(1) utility. truncate Change the length of the segments. Argument to the -s option specifies new length. The human-friendly 'k', 'm', 'g' suf- fixes can be used, see expand_number(3). If the option is not specified, assumed length is zero. For some commands, the following options may be provided: -h If specified, requests human-readable display of size, see humanize_number(3). -n Prevent translation of owner and group into symbolic names using name-switch services, instead the raw numeric values are printed. EXIT STATUS The posixshmcontrol utility exits 0 on success, and >0 if an error oc- curs. EXAMPLES +o To show content of the shared memory segment with the path /1, use the command posixshmcontrol dump /1 | hexdump -C +o To create a segment with the path /2 and then enlarge it to 1M, use the sequence of commands posixshmcontrol create /2 posixshmcontrol truncate -s 1m /2 SEE ALSO hexdump(1), stat(1), ftruncate(2), read(2), shm_open(2), shm_unlink(2), stat(2), expand_number(3), humanize_number(3), sysctl(3) HISTORY The posixshmcontrol command appeared in FreeBSD 12.1. AUTHORS The posixshmcontrol command and this manual page were written by Konstantin Belousov <kib@freebsd.org> under sponsorship from The FreeBSD Foundation. FreeBSD 13.0 March 18, 2020 FreeBSD 13.0
NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | EXAMPLES | SEE ALSO | HISTORY | AUTHORS
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