shm_open(2)							System Calls Manual						       shm_open(2)

NAME

       shm_open - create/open a shared memory object

SYNOPSIS

DESCRIPTION

       The  system  call  establishes a connection between a shared memory object and a file descriptor.  It creates an open file description that
       corresponds to the shared memory object and returns a file descriptor that refers to that open  file  description.   This  file	descriptor
       (which  is the lowest numbered file descriptor not currently open for that process) is used by other functions to refer to that shared mem-
       ory object.

       The name argument points to the shared memory object name, and must conform to the general construction rules for a pathname.

       The oflag argument is the bitwise inclusive OR of the flags listed under and (these flags are defined in the header file

       The new file descriptor has the flag set, and consequently does not remain open across system calls.

   Read-Write Flags
       The value of oflag must be composed by taking the inclusive OR of exactly one of the following flags:

	      Open for read access only.

	      Open for read and write access.

   General Flags
       Any combination of the following flags may also be used in setting the value of oflag.

	      If the shared memory object exists, this flag will have no effect, except as
			     noted under below.  Otherwise the shared memory object is created; the shared memory object's user ID is set  to  the
			     effective	user  ID  of  the  process;  the  shared  memory object's group ID is set to the effective group ID of the
			     process.  The shared memory object's permission bits is set to the value of the mode argument except those set in the
			     file mode creation mask of the process.  The new shared memory object will have a size of zero.

	      If	     and  are  set  in	oflag  and the named shared memory object exists, will fail.  The flag is ignored if is not set in
			     oflag.

	      If the shared memory object exists, and it is successfully opened for reading
			     and writing set in oflag), the object will be truncated to zero length.  The mode and owner shall remain unchanged by
			     this function call.

RETURN VALUE

       returns the following values:

	      n    Successful completion.  n is the lowest numbered unused file descriptor for the process.

	      Failure.
		   is set to indicate the error.

ERRORS

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

	      The shared memory object exists and the permissions specified by
			     oflag  are denied, or the shared memory object does not exist and permission to create the it is denied, or is speci-
			     fied and write permission is denied.

	      The	     and are set in oflag and the named shared memory object already exists.

	      The	     operation was interrupted by a signal.

	      The	     operation is not supported for the given name.

	      Too many file descriptors are currently in use by this process.

	      The length of the
			     name string exceeds or the length of a (pathname) component of the name string exceeds while is in effect.

	      Too many shared memory objects are currently open in the system.

	      The	     flag is not set in oflag and the named shared memory object does not exist.

	      There are insufficient resources for the creation of the new shared memory
			     object.

	      is not supported by the implementation.

SEE ALSO

       shm_unlink(2), close(2), mmap(2), munmap(2), privileges(5).

STANDARDS CONFORMANCE

																       shm_open(2)