semctl(2)							System Calls Manual							 semctl(2)

NAME

       semctl() - semaphore control operations

SYNOPSIS

DESCRIPTION

       The system call provides a variety of semaphore control operations as specified by cmd.	The fourth argument is optional and depends on the
       operation requested.  If present, it must be of type which the application program must explicitly declare.  For the meaning of unspecified
       variables, see in glossary(9).

       The following values for cmd are executed with respect to the semaphore specified by semid and semnum:

	      Returns the semaphore value.
			   Requires semaphore Read permission.

	      Sets the value of the semaphore
			   to  arg.val,  where	arg  is the fourth argument of taken as a When this cmd is successfully executed, the semadj value
			   corresponding to the specified semaphore in all processes is cleared.  Requires semaphore Alter permission.

	      Returns the pid of the last process that performed a
			   semaphore operation on this semaphore.  Requires semaphore Read permission.

	      Returns count of the number of processes that are
			   currently suspended awaiting this semaphore's value to become greater than its current value.  Requires semaphore  Read
			   permission.

	      Returns count of the number of processes that are
			   currently suspended awaiting this semaphore's value to become zero.	Requires semaphore Read permission.

       The following values for cmd return and set, respectively, every semaphore in the set of semaphores.

	      Place semaphore value into array pointed to by
			   arg.array, where arg is the fourth argument of taken as a Requires semaphore Read permission.

	      Set semaphore value
			   according  to  the  array pointed to by arg.array, where arg is the fourth argument of taken as a When this cmd is suc-
			   cessfully executed, the semadj values corresponding to each specified semaphore in all processes are cleared.  Requires
			   semaphore Alter permission.

       The following values for cmd are also available:

	      Place the current value of each member
			   of  the data structure associated with semid into the structure pointed to by arg.buf, where arg is the fourth argument
			   of taken as a The contents of this structure are defined in glossary(9).  Requires semaphore Read permission.

	      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, where arg  is  the  fourth  argument	of
			   taken as a

			   This cmd can only be executed by a process that has an effective user ID equal to either that of a user with the privi-
			   lege or to the value of either or in the data structure associated with semid.

	      Remove the semaphore identifier specified by
			   semid from the system and destroy the set of semaphores and data structure associated with it.  This cmd  can  only	be
			   executed  by  a process that has an effective user ID equal to either that of a user with the privilege or to the value
			   of either or in the data structure associated with semid.

   Security Restrictions
       Some or all of the actions associated with this system call are subject to compartmental restrictions. See compartments(5) for more  infor-
       mation  about  compartmentalization on systems that support that feature.  Compartmental restrictions can be overridden if the process pos-
       sesses the privilege (PRIV_COMMALLOWED).  Processes owned by the superuser may not have this privilege.	Processes owned by  any  user  may
       have this privilege, depending on system configuration.

       Some  or  all  of the actions associated with this system call require one or more privileges.  Processes owned by the superuser have many,
       though not all, privileges.  Processes owned by other users may have privilege(s), depending on system  configuration.	See  privileges(5)
       for more information about privileged access on systems that support fine-grained privileges.

RETURN VALUE

       Upon successful completion, returns a value based on cmd.

       All others return

       If it fails, it returns and sets to indicate the error.

ERRORS

       If fails, it sets to one of the following values:

	      Operation permission is denied to the calling process (see
			   in glossary(9).

	      cmd	   is or and arg is an invalid pointer.

	      semid	   is not a valid semaphore identifier.

	      semnum	   is less than zero or greater than or equal

	      cmd	   is not a valid command, or the command contains invalid parameters.

	      cmd	   is  equal to or and the process does not have an effective user ID equal to either that of a user with the privilege or
			   to the value of either or in the data structure associated with semid.

	      cmd	   is or and the value to which semaphore value is to be set is greater than the system imposed maximum.

EXAMPLES

       The following call to initializes the set of 4 semaphores to the values 0, 1, 0, and 1 respectively.  This example assumes the process  has
       a  valid  semid representing a set of 4 semaphores as shown in the semget(2) manual entry.  For an example of performing "P" and "V" opera-
       tions on the semaphores below, refer to semop(2).

SEE ALSO

       ipcrm(1), ipcs(1), semget(2), semop(2), privileges(5), glossary(9).

STANDARDS CONFORMANCE

																	 semctl(2)