SHMCTL(2)						      BSD 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 identified by shmid:

     IPC_STAT	  Fetch the segment's struct shmid_ds, storing it in the memory 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 effective uid must match either shm_perm.uid or shm_perm.cuid, or it must have supe-
		  ruser privileges.

     IPC_RMID	  Removes the segment from the system.	The removal will not take effect until all processes having attached the segment have
		  exited; however, once the IPC_RMID operation has taken place, no further processes will be allowed to attach the segment.  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 privileges.

     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)

BSD
								   July 17, 1995							       BSD