shmop(2)							System Calls Manual							  shmop(2)

NAME

       shmat(), shmdt() - shared memory operations

SYNOPSIS

DESCRIPTION

       attaches  the  shared  memory  segment  associated  with the shared memory identifier specified by shmid to the data segment of the calling
       process.

       The segment is attached for reading if (shmflg is "true"; otherwise, it is attached for reading and writing.  It is not possible to  attach
       a segment for write only.

       If the shared memory segment has never been attached to by any process prior to the current call, shmaddr must be specified as zero and the
       segment is attached at a location selected by the operating system.  That location is identical in all processes accessing that shared mem-
       ory object.  Once the operating system selects a location for a shared memory segment, the same location will be used across any subsequent
       and calls on the segment until it is removed by the operation of See exceptions for MPAS processes below.

       If this is not the first call on the shared memory segment throughout the system, shmaddr must either be zero or contain a nonzero  address
       that is identical to the one returned from previous calls for that segment.  Even if no processes are currently attached to the segment, as
       long as the segment has been attached before, the same rule applies. See exceptions for MPAS processes below.

       If the calling process is already attached to the shared memory segment, fails and returns regardless of what value is passed  in  shmaddr.
       See exceptions for MPAS processes below.

       detaches from the calling process's data segment the shared memory segment located at the address specified by shmaddr.

   Exceptions for MPAS Processes
       On  Itanium(R)-based  platforms,  MPAS  (Mostly	Private Address Space) processes are not restricted to passing in zero or a fixed value to
       calls to MPAS processes may pass in other addresses.  The call may fail or succeed due to implementation dependent reasons.  MGAS processes
       have  all  the  restrictions  outlined  above.	In addition, an MGAS process may not assume that it can attach at the address that an MPAS
       process can use to attach to the same segment.

       An MPAS process may be able to attach to the same shared memory segment multiple times.	Success or failure of such an operation is  imple-
       mentation dependent.  Failure will be indicated by a return value of

       An MPAS process should specify or flags in the call to These follow the same rules as such flags passed to shmget(2).

       See the for details.

RETURN VALUE

       returns the following values:

	      Successful completion.
		     n is the data segment start address of the attached shared memory segment.
	      Failure.
		     The  shared memory segment is not attached.  is set to indicate the error.  The symbol is defined in the header No successful
		     return from will return the value

       returns the following values:

	      Successful completion.
	      Failure.
		     is set to indicate the error.

ERRORS

       If fails, is set to one of the following values.

	      [EACCES]	     Operation permission is denied to the calling process.

	      [EINVAL]	     shmid is not a valid shared memory identifier, (possibly because the shared memory segment was already removed  using
			     shmctl(2) with or the calling process is already attached to shmid.

	      [EINVAL]	     shmaddr  is  not  zero  and the machine does not permit nonzero values, or shmaddr is not equal to the current attach
			     location for the shared memory segment.

	      [ENOMEM]	     The available data space is not large enough to accommodate the shared memory segment.

	      [EMFILE]	     The number of shared memory segments attached to the calling process exceed the system-imposed limit.

       If fails, is set to one of the following values.

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

EXAMPLES

       The following call to attaches the shared memory segment to the process.  This example assumes the process has a valid shmid, which can	be
       obtained by calling shmget(2).

       The following call to then detaches the shared memory segment.

SEE ALSO

       ipcs(1), exec(2), exit(2), fork(2), ftok(3C), shmctl(2), shmget(2), privileges(5).

       in

STANDARDS CONFORMANCE

																	  shmop(2)