semctl(2)							   System Calls 							 semctl(2)

NAME

       semctl - semaphore control operations

SYNOPSIS

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

       int semctl(int semid, int semnum, int cmd, ...);

DESCRIPTION

       The  semctl()  function	provides a variety of semaphore control operations as specified by cmd. The fourth argument is optional, depending
       upon the operation  requested.  If required, it is of type  union semun, which must be explicitly declared by the application program.

       union semun {
	       int	       val;
	       struct semid_ds *buf;
	       ushort_t        *array;
       } arg ;

       The permission required for a semaphore operation is given as {token}, where token is the type of permission needed.  The types of  permis-
       sion are interpreted as follows:

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

       See  the  Semaphore  Operation  Permissions subsection of the DEFINITIONS section of intro(2) for more information. The following semaphore
       operations as specified by cmd are executed with respect to the semaphore specified by semid and semnum.

       GETVAL	       Return the value of  semval (see intro(2)). {READ}

       SETVAL	       Set the value of  semval to arg.val. {ALTER} When this command is successfully executed, the semadj value corresponding	to
		       the specified semaphore in all processes is cleared.

       GETPID	       Return the value of (int) sempid. {READ}

       GETNCNT	       Return the value of semncnt. {READ}

       GETZCNT	       Return the value of semzcnt. {READ}

       The following operations return and set, respectively, every semval in the set of semaphores.

       GETALL	       Place semvals into array pointed to by arg.array. {READ}

       SETALL	       Set  semvals  according	to  the array pointed to by arg.array. {ALTER}. When this cmd is successfully executed, the semadj
		       values corresponding to each specified semaphore in all processes are cleared.

       The following operations are also available.

       IPC_STAT        Place the current value of each member of the data structure associated	with  semid  into  the	structure  pointed  to	by
		       arg.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 semid to the corresponding value found in the
		       structure pointed to by arg.buf:

		       sem_perm.uid
		       sem_perm.gid
		       sem_perm.mode  /* access permission bits only */

		       This command can be executed only by a process that has either the {PRIV_IPC_OWNER} privilege or an effective user ID equal
		       to  the	value  of  msg_perm.cuid  or  msg_perm.uid  in	the  data structure associated with msqid. Only a process with the
		       {PRIV_SYS_IPC_CONFIG} privilege can raise the value of msg_qbytes.

       IPC_RMID        Remove the semaphore identifier specified by semid from the system and destroy the set of  semaphores  and  data  structure
		       associated  with it. This command can be executed only by a process that has the {PRIV_IPC_OWNER} privilege or an effective
		       user ID equal to the value of sem_perm.cuid or sem_perm.uid in the data structure associated with semid.

RETURN VALUES

       Upon successful completion, the value returned depends on cmd as follows:

       GETVAL	       the value of semval

       GETPID	       the value of (int) sempid

       GETNCNT	       the value of semncnt

       GETZCNT	       the value of semzcnt

       All other successful completions return	0; otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       The semctl() function will fail if:

       EACCES	       Operation permission is denied to the calling process (see intro(2)).

       EFAULT	       The source or target is not a valid address in the user process.

       EINVAL	       The semid argument is not a valid semaphore identifier; the semnum argument is less than 0 or greater than sem_nsems -1; or
		       the cmd argument is not a valid command or is IPC_SET and sem_perm.uid or sem_perm.gid is not valid.

       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
		       sem_perm.cuid or sem_perm.uid in the data structure associated with semid, and {PRIV_IPC_OWNER}	is  not  asserted  in  the
		       effective set of the calling process.

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

       ERANGE	       The cmd argument is SETVAL or SETALL and the value to which semval is to be set is greater than the system imposed maximum.

ATTRIBUTES

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

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

SEE ALSO

       ipcs(1), intro(2), semget(2), semop(2), attributes(5), privileges(5), standards(5)

SunOS 5.10							    1 Feb 2003								 semctl(2)