.\" and Copyright 1993 Giorgio Ciucci <giorgio@crcc.it>
.\" and Copyright 2004, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" Modified 1993-07-28, Rik Faith <faith@cs.unc.edu>
.\" Modified 1993-11-28, Giorgio Ciucci <giorgio@crcc.it>
.\" attaches to a segment that has already been marked for deletion.
.\" 2005-08-02, mtk: Added IPC_INFO, SHM_INFO, SHM_STAT descriptions.
.\"
-.TH SHMCTL 2 2008-08-07 "Linux" "Linux Programmer's Manual"
+.TH SHMCTL 2 2014-02-07 "Linux" "Linux Programmer's Manual"
.SH NAME
-shmctl \- shared memory control
+shmctl \- System V shared memory control
.SH SYNOPSIS
.ad l
.B #include <sys/ipc.h>
.BR shmctl ()
performs the control operation specified by
.I cmd
-on the shared memory segment whose identifier is given in
+on the System\ V shared memory segment whose identifier is given in
.IR shmid .
.PP
The
.PP
The
.I ipc_perm
-structure is defined in \fI<sys/ipc.h>\fP as follows
+structure is defined as follows
(the highlighted fields are settable using
.BR IPC_SET ):
.PP
.TP
.B IPC_RMID
Mark the segment to be destroyed.
-The segment will only actually be destroyed
-after the last process detaches it (i.e., when the
+The segment will actually be destroyed
+only after the last process detaches it (i.e., when the
.I shm_nattch
member of the associated structure
.I shmid_ds
is zero).
-The caller must be the owner or creator, or be privileged.
+The caller must be the owner or creator of the segment, or be privileged.
+The
+.I buf
+argument is ignored.
+.IP
If a segment has been marked for destruction, then the (nonstandard)
.B SHM_DEST
flag of the
field in the associated data structure retrieved by
.B IPC_STAT
will be set.
-.PP
+.IP
The caller \fImust\fP ensure that a segment is eventually destroyed;
otherwise its pages that were faulted in will remain in memory or swap.
+.IP
+See also the description of
+.I /proc/sys/kernel/shm_rmid_forced
+in
+.BR proc (5).
.TP 10
.BR IPC_INFO " (Linux-specific)"
-Returns information about system-wide shared memory limits and
+Return information about system-wide shared memory limits and
parameters in the structure pointed to by
.IR buf .
This structure is of type
.nf
.in +4n
-struct shminfo {
+struct shminfo {
unsigned long shmmax; /* Maximum segment size */
unsigned long shmmin; /* Minimum segment size;
always 1 */
for details.
.TP
.BR SHM_INFO " (Linux-specific)"
-Returns a
+Return a
.I shm_info
structure whose fields contain information
about system resources consumed by shared memory.
.fi
.TP
.BR SHM_STAT " (Linux-specific)"
-Returns a
+Return a
.I shmid_ds
structure as for
.BR IPC_STAT .
.\" be applied to a segment, regardless of ownership of the segment.
.\" This was a botch-up in the move to RLIMIT_MEMLOCK, and was fixed
.\" in 2.6.10. MTK, May 2005
-.SH "RETURN VALUE"
+.SH RETURN VALUE
A successful
.B IPC_INFO
or
(Since Linux 2.6.9, this error can also occur if the
.B RLIMIT_MEMLOCK
is 0 and the caller is not privileged.)
-.SH "CONFORMING TO"
+.SH CONFORMING TO
SVr4, POSIX.1-2001.
.\" SVr4 documents additional error conditions EINVAL,
.\" ENOENT, ENOSPC, ENOMEM, EEXIST. Neither SVr4 nor SVID documents
.\" an EIDRM error condition.
.SH NOTES
+The inclusion of
+.I <sys/types.h>
+and
+.I <sys/ipc.h>
+isn't required on Linux or by any version of POSIX.
+However,
+some old implementations required the inclusion of these header files,
+and the SVID also documented their inclusion.
+Applications intended to be portable to such old systems may need
+to include these header files.
+.\" Like Linux, the FreeBSD man pages still document
+.\" the inclusion of these header files.
+
The
.BR IPC_INFO ,
.B SHM_STAT
and
.B SHM_INFO
operations are used by the
-.BR ipcs (8)
+.BR ipcs (1)
program to provide information on allocated resources.
-In the future these may modified or moved to a /proc file system
-interface.
+In the future, these may modified or moved to a
+.I /proc
+filesystem interface.
Linux permits a process to attach
.RB ( shmat (2))
a shared memory segment that has already been marked for deletion
using
.IR shmctl(IPC_RMID) .
-This feature is not available on other Unix implementations;
+This feature is not available on other UNIX implementations;
portable applications should avoid relying on it.
Various fields in a \fIstruct shmid_ds\fP were typed as
.B IPC_64
flag in
.IR cmd .)
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR mlock (2),
.BR setrlimit (2),
.BR shmget (2),
.BR shmop (2),
.BR capabilities (7),
.BR svipc (7)
+.SH COLOPHON
+This page is part of release 3.79 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.
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