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SHMGET(2)		       System Calls Manual		       SHMGET(2)

NAME
     shmget -- obtain a shared memory identifier

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/shm.h>

     int
     shmget(key_t key, size_t size, int flag);

DESCRIPTION
     Based  on	the values of key and flag, shmget() returns the identifier of a
     newly created or previously existing shared memory  segment.   The  key  is
     analogous	to  a  filename:  it provides a handle that names an IPC object.
     There are three ways to specify a key:

     *	 IPC_PRIVATE may be specified, in which case a new IPC	object	will  be
	 created.

     *	 An  integer  constant may be specified.  If no IPC object corresponding
	 to key is specified and the IPC_CREAT bit is set in  flag,  a	new  one
	 will be created.

     *	 The ftok(3) may be used to generate a key from a pathname.

     The  mode	of  a newly created IPC object is determined by which are set by
     ORing these constants into the flag argument:

     0400
       Read access for owner.

     0200
       Write access for owner.

     0040
       Read access for group.

     0020
       Write access for group.

     0004
       Read access for other.

     0002
       Write access for other.

     When creating a new shared memory segment, size indicates the desired  size
     of  the new segment in bytes.  The size of the segment may be rounded up to
     a multiple convenient to the kernel (i.e., the page size).

RETURN VALUES
     Upon successful completion, shmget() returns the positive	integer  identi-
     fier  of  a shared memory segment.  Otherwise, -1 is returned and errno set
     to indicate the error.

ERRORS
     The shmget() system call will fail if:

     [EINVAL]		Size specified is greater than the size  of  the  previ-
			ously existing segment.  Size specified is less than the
			system	imposed  minimum, or greater than the system im-
			posed maximum.

     [ENOENT]		No shared memory segment was  found  matching  key,  and
			IPC_CREAT was not specified.

     [ENOSPC]		The  kernel was unable to allocate enough memory to sat-
			isfy the request.

     [EEXIST]		IPC_CREAT and IPC_EXCL were specified, and a shared mem-
			ory segment corresponding to key already exists.

SEE ALSO
     shmat(2), shmctl(2), shmdt(2), ftok(3)

FreeBSD ports 15.quarterly	  March 4, 2018 		       SHMGET(2)

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