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Linux 2.6 - man page for shmctl (linux section 3posix)

SHMCTL(P)			    POSIX Programmer's Manual				SHMCTL(P)

NAME
       shmctl - XSI shared memory control operations

SYNOPSIS
       #include <sys/shm.h>

       int shmctl(int shmid, int cmd, struct shmid_ds *buf);

DESCRIPTION
       The  shmctl()  function	operates on XSI shared memory (see the Base Definitions volume of
       IEEE Std 1003.1-2001, Section 3.340, Shared Memory Object). It is unspecified whether this
       function  interoperates with the realtime interprocess communication facilities defined in
       Realtime .

       The shmctl() function provides a variety of shared memory control operations as	specified
       by cmd. The following values for cmd are available:

       IPC_STAT
	      Place  the  current  value of each member of the shmid_ds data structure associated
	      with shmid into the structure pointed to by buf. The contents of the structure  are
	      defined in <sys/shm.h>.

       IPC_SET
	      Set  the	value  of the following members of the shmid_ds data structure associated
	      with shmid to the corresponding value found in the structure pointed to by buf:

	      shm_perm.uid
	      shm_perm.gid
	      shm_perm.mode    Low-order nine bits.

       IPC_SET can only be executed by a process that has an effective user ID	equal  to  either
       that  of  a  process  with  appropriate	privileges  or	to  the value of shm_perm.cuid or
       shm_perm.uid in the shmid_ds data structure associated with shmid.

       IPC_RMID
	      Remove the shared memory identifier specified by shmid from the system and  destroy
	      the  shared memory segment and shmid_ds data structure associated with it. IPC_RMID
	      can only be executed by a process that has an effective user  ID	equal  to  either
	      that  of	a process with appropriate privileges or to the value of shm_perm.cuid or
	      shm_perm.uid in the shmid_ds data structure associated with shmid.

RETURN VALUE
       Upon successful completion, shmctl() shall return 0; otherwise, it shall return -1 and set
       errno to indicate the error.

ERRORS
       The shmctl() function shall fail if:

       EACCES The  argument  cmd  is equal to IPC_STAT and the calling process does not have read
	      permission; see XSI Interprocess Communication .

       EINVAL The value of shmid is not a valid shared memory identifier, or the value of cmd  is
	      not a valid command.

       EPERM  The  argument  cmd is equal to IPC_RMID or IPC_SET and the effective user ID of the
	      calling process is not equal to that of a process with appropriate  privileges  and
	      it is not equal to the value of shm_perm.cuid or shm_perm.uid in the data structure
	      associated with shmid.

       The shmctl() function may fail if:

       EOVERFLOW
	      The cmd argument is IPC_STAT and the gid or uid value is too large to be stored  in
	      the structure pointed to by the buf argument.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The  POSIX  Realtime  Extension defines alternative interfaces for interprocess communica-
       tion. Application developers who need to use IPC should design their applications so  that
       modules	using  the IPC routines described in XSI Interprocess Communication can be easily
       modified to use the alternative interfaces.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       XSI Interprocess Communication , Realtime , shmat() , shmdt() , shmget()  ,  shm_open()	,
       shm_unlink() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/shm.h>

COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					SHMCTL(P)


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