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

NAME
     semget -- obtain a semaphore id

SYNOPSIS
     ##include <>
     ##include <>
     ##include <>

     int
     semget(keyt 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:

     ]o   IPCPRIVATE may be specified, in which case a new IPC object will be
         created.

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

     ]o   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:

     SEMR         Read access for user.

     SEMA         Alter access for user.

     (SEMR>>3)    Read access for group.

     (SEMA>>3)    Alter access for group.

     (SEMR>>6)    Read access for other.

     (SEMA>>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.

ERORS
     The semget() system call will fail if:

     [EACES]           Access permission failure.

     [EXIST]           IPCREAT and IPCEXCL 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 semidds.

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

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

BSD                           September 12, 1995                           BSD