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SEMGET(2)		    BSD System Calls Manual		     SEMGET(2)

NAME
     semget — obtain a semaphore id

LIBRARY
     Standard C Library (libc, -lc)

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

     int
     semget(key_t key, int nsems, int flag);

DESCRIPTION
     Based on the values of key and flag, semget() returns the identifier of a
     newly created or previously existing set of semaphores.  The key is anal‐
     ogous to a filename: it provides a handle that names an IPC object.
     There are three ways to specify a key:

     ·	 IPC_PRIVATE may be specified, in which case a new IPC object will be
	 created.

     ·	 An integer constant may be specified.	If no IPC object corresponding
	 to key is specified and the IPC_CREAT bit is set in flag, a new one
	 will be created.

     ·	 The ftok(3) function may be used to generate a key from a pathname.

     The mode of a newly created IPC object is determined by OR'ing the fol‐
     lowing constants into the flag argument:

     SEM_R	   Read access for user.

     SEM_A	   Alter access for user.

     (SEM_R>>3)	   Read access for group.

     (SEM_A>>3)	   Alter access for group.

     (SEM_R>>6)	   Read access for other.

     (SEM_A>>6)	   Alter access for other.

     If a new set of semaphores is being created, nsems is used to indicate
     the number of semaphores the set should contain.  Otherwise, nsems may be
     specified as 0.

RETURN VALUES
     The semget() system call returns the id of a semaphore set if successful;
     otherwise, -1 is returned and errno is set to indicate the error.

ERRORS
     The semget() system call will fail if:

     [EACCES]		Access permission failure.

     [EEXIST]		IPC_CREAT and IPC_EXCL were specified, and a semaphore
			set corresponding to key already exists.

     [EINVAL]		The number of semaphores requested exceeds the system
			imposed maximum per set.

     [ENOSPC]		Insufficiently many semaphores are available.

     [ENOSPC]		The kernel could not allocate a struct semid_ds.

     [ENOENT]		No semaphore set was found corresponding to key, and
			IPC_CREAT was not specified.

SEE ALSO
     semctl(2), semop(2), ftok(3)

BSD			      September 12, 1995			   BSD
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