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SHMCTL(2)		  FreeBSD System Calls Manual		     SHMCTL(2)

NAME
     shmctl -- shared memory control

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

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

DESCRIPTION
     Performs the action specified by cmd on the shared	memory segment identi-
     fied by shmid:

     IPC_STAT	  Fetch	the segment's struct shmid_ds, storing it in the mem-
		  ory pointed to by buf.

     IPC_SET	  Changes the shm_perm.uid, shm_perm.gid, and shm_perm.mode
		  members of the segment's struct shmid_ds to match those of
		  the struct pointed to	by buf.	 The calling process's effec-
		  tive uid must	match either shm_perm.uid or shm_perm.cuid, or
		  it must have superuser privileges.

     IPC_RMID	  Removes the segment from the system.	The removal will not
		  take effect until all	processes having attached the segment
		  have exited.	For the	operation to succeed, the calling
		  process's effective uid must match shm_perm.uid or
		  shm_perm.cuid, or the	process	must have superuser privi-
		  leges.  If the kern.ipc.shm_allow_removed sysctl(3) variable
		  is set to 0, once the	IPC_RMID operation has taken place, no
		  further processes will be allowed to attach the segment.

     The shmid_ds structure is defined as follows:

     struct shmid_ds {
	 struct	ipc_perm shm_perm;   /*	operation permission structure */
	 size_t		 shm_segsz;  /*	size of	segment	in bytes */
	 pid_t		 shm_lpid;   /*	process	ID of last shared memory op */
	 pid_t		 shm_cpid;   /*	process	ID of creator */
	 int		 shm_nattch; /*	number of current attaches */
	 time_t		 shm_atime;  /*	time of	last shmat() */
	 time_t		 shm_dtime;  /*	time of	last shmdt() */
	 time_t		 shm_ctime;  /*	time of	last change by shmctl()	*/
     };

RETURN VALUES
     The shmctl() function returns the value 0 if successful; otherwise	the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The shmctl() system call will fail	if:

     [EINVAL]		Invalid	operation, or no shared	memory segment was
			found corresponding to shmid.

     [EPERM]		The calling process's effective	uid does not match the
			uid of the shared memory segment's owner or creator.

     [EACCES]		Permission denied due to mismatch between operation
			and mode of shared memory segment.

SEE ALSO
     shmat(2), shmdt(2), shmget(2), ftok(3)

FreeBSD	11.0		       October 10, 2015			  FreeBSD 11.0

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO

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