SEM(4) Device Drivers Manual SEM(4)

sem
POSIX semaphores

The POSIX semaphore code is included by default in all kernels.

The sem facility provides system calls used by the standard C library (libc) to implement POSIX semaphores.

config(1), sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_post(3), sem_wait(3), options(4)

The sem facility appeared as a kernel option in NetBSD 2.0 and became non-optional in NetBSD 7.0.
August 20, 2015 NetBSD 9.4