SHMAT(2)						      BSD System Calls Manual							  SHMAT(2)

NAME

     shmat, shmdt -- map/unmap shared memory

SYNOPSIS

     #include <sys/shm.h>

     void *
     shmat(int shmid, const void *shmaddr, int shmflg);

     int
     shmdt(const void *shmaddr);

DESCRIPTION

     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 existant until it is
     removed by a call to shmctl(2) with the IPC_RMID command.

RETURN VALUES

     shmat() returns the address at which the shared memory segment has been mapped into the calling process' address space when successful,
     shmdt() returns 0 on successful completion. Otherwise, a value of -1 is returned, and the global variable errno is set to indicate the error.

ERRORS

     The shmat() system call will fail if:

     [EACCES]		The calling process has no permission to access this shared memory segment.

     [EINVAL]		shmid is not a valid shared memory identifier.	shmaddr specifies an illegal address.

     [EMFILE]		The number of shared memory segments has reached the system-wide limit.

     [ENOMEM]		There is not enough available data space for the calling process to map the shared memory segment.

     The shmdt() system call will fail if:

     [EINVAL]		shmaddr is not the start address of a mapped shared memory segment.

LEGACY SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     The include files <sys/types.h> and <sys/ipc.h> are necessary for both functions.

SEE ALSO

     mmap(2), shmctl(2), shmget(2), compat(5)

BSD
								  August 17, 1995							       BSD