shmctl(2)							   System Calls 							 shmctl(2)

NAME

       shmctl - shared memory control operations

SYNOPSIS

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

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

DESCRIPTION

       The shmctl() function provides a variety of shared memory control operations as specified by cmd. The permission required for a shared mem-
       ory control operation is given as {token}, where token is the type of permission needed. The types of permission are  interpreted  as  fol-
       lows:

	 00400	  READ by user
	 00200	  WRITE by user
	 00040	  READ by group
	 00020	  WRITE by group
	 00004	  READ by others
	 00002	  WRITE by others

       See the Shared Memory Operation Permissions section of Intro(2) for more information.

       The following operations require the specified tokens:

       IPC_STAT      Place  the current value of each member of the data structure associated with shmid into the structure pointed to by buf. The
		     contents of this structure are defined in Intro(2). {READ}

       IPC_SET	     Set the value of the following members of the 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  /* access permission bits only */

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

       IPC_RMID      Remove the shared memory identifier specified by shmid from the system. The segment referenced  by  the  identifier  will	be
		     destroyed	when  all  processes  with  the segment attached have either detached the segment or exited. If the segment is not
		     attached to any process when IPC_RMID is invoked, it will be destroyed immediately. This command can be executed  only  by  a
		     process  that  has  appropriate privileges or an effective user ID equal to the value of shm_perm.cuid or shm_perm.uid in the
		     data structure associated with shmid.

       SHM_LOCK      Lock the shared memory segment specified by shmid in memory. This command can be executed only by a process that  has  appro-
		     priate privileges.

       SHM_UNLOCK    Unlock  the  shared  memory  segment  specified by shmid. This command can be executed only by a process that has appropriate
		     privileges.

       A shared memory segment must be explicitly removed using IPC_RMID before the system can deallocate it and the resources it uses.

RETURN VALUES

       Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       The shmctl() function will fail if:

       EACCES	    The cmd argument is equal to IPC_STAT and {READ} operation permission is denied to the calling process.

       EFAULT	    The buf argument points to an illegal address.

       EINVAL	    The shmid argument is not a valid shared memory identifier; or the cmd argument is not a  valid  command  or  is  IPC_SET  and
		    shm_perm.uid or shm_perm.gid is not valid.

       ENOMEM	    The  cmd  argument is equal to SHM_LOCK and there is not enough memory, or the operation would exceed a limit or resource con-
		    trol on locked memory.

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

       EPERM	    The cmd argument is equal to IPC_RMID or IPC_SET, the effective user ID of the calling process is not equal to  the  value	of
		    shm_perm.cuid  or shm_perm.uid in the data structure associated with shmid, and {PRIV_IPC_OWNER} is not asserted in the effec-
		    tive set of the calling process.

		    The cmd argument is equal to SHM_LOCK or SHM_UNLOCK and {PRIV_PROC_LOCK_MEMORY} is not asserted in the effective  set  of  the
		    calling process.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ipcs(1), Intro(2), shmget(2), shmop(2), attributes(5), privileges(5), standards(5)

SunOS 5.11							    10 Apr 2007 							 shmctl(2)