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SEMGET(2)		       System Calls Manual		       SEMGET(2)

NAME
     semget -- obtain a semaphore id

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #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  analo-
     gous  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 ORing these con-
     stants into the flag argument:

     0400
       Read access for user.

     0200
       Alter access for user.

     0040
       Read access for group.

     0020
       Alter access for group.

     0004
       Read access for other.

     0002
       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 spec-
     ified 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.

     [EINVAL]		A semaphore set corresponding to key already exists  and
			contains fewer semaphores than nsems.

     [EINVAL]		A  semaphore set corresponding to key does not exist and
			nsems is 0 or negative.

     [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)

FreeBSD ports 15.quarterly	  March 4, 2018 		       SEMGET(2)

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