shmget man page on BSDi

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SHMGET(2)		    BSD Programmer's Manual		     SHMGET(2)

NAME
     shmget - obtain a shared memory identifier

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

     int
     shmget(key_t key, int 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:

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

     o	 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.

     o	 ftok() may be used to generate a key from a pathname.	See ftok(3).

     The mode of a newly created IPC object is determined by OR'ing the fol-
     lowing constants into the flag parameter:

     SHM_R	   Read access for user.

     SHM_W	   Write access for user.

     (SHM_R>>3)	   Read access for group.

     (SHM_W>>3)	   Write access for group.

     (SHM_R>>6)	   Read access for other.

     (SHM_W>>6)	   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
     Shmget() will fail if:

     [EINVAL]	   Size specified is greater than the size of the previously
		   existing segment.  Size specified is less than the system
		   imposed minimum, or greater than the system imposed maxi-
		   mum.

     [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 satisfy

		   the request.

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

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

4th Berkeley Distribution	 July 3, 1996				     2
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