shmat() maps the shared memory segment associated with the shared memory identifier
shmid into the address space of the calling process. The address at which the segment is mapped is determined by the
shmaddr parameter. If it is equal to 0, the system will pick an address itself. Otherwise, an attempt is made to map the shared memory segment at the address
shmaddr specifies. If
SHM_RND is set in
shmflg, the system will round the address down to a multiple of
SHMLBA bytes (
SHMLBA is defined in
<sys/shm.h>).
A shared memory segment can be mapped read-only by specifying the
SHM_RDONLY flag in
shmflg.
shmdt() unmaps the shared memory segment that is currently mapped at
shmaddr from the calling process' address space.
shmaddr must be a value returned by a prior
shmat() call. A shared memory segment will remain in existence until it is removed by a call to
shmctl(2) with the
IPC_RMID command.