Provided by:
freebsd-manpages_6.2-1_all 
NAME
sem - POSIX semaphores
SYNOPSIS
To link into the kernel:
options P1003_1B_SEMAPHORES
To load as a kernel loadable module:
kldload sem
DESCRIPTION
The sem facility provides system calls used by the standard C library
(libc) to implement POSIX semaphores. It is available both as a kernel
option for static inclusion and as a dynamic kernel module.
SEE ALSO
sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_post(3),
sem_wait(3), config(8), kldload(8), kldunload(8)
HISTORY
The sem facility appeared as a kernel option in FreeBSD 3.0. The sem
kernel module appeared in FreeBSD 5.0.