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POSIXSHMCONTROL(1)	  BSD 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 /q | 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 13.0.

AUTHORS
     The posixshmcontrol command and this manual page were written by
     Konstantin	Belousov <kib@freebsd.org> under sponsorship from The FreeBSD
     Foundation.

BSD				 May 30, 2019				   BSD

NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | EXAMPLES | SEE ALSO | HISTORY | AUTHORS

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