SEMGET(2)                 FreeBSD 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
     analogous 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
     constants 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
     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.

     [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 13.1-RELEASE-p6          March 4, 2018         FreeBSD 13.1-RELEASE-p6