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.

       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
		       effective 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 5.10							    1 Feb 2003								 shmctl(2)