shmget(2) [freebsd man page]

SHMGET(2)						      BSD System Calls Manual							 SHMGET(2)

NAME

     shmget -- obtain a shared memory identifier

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

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

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

     The mode of a newly created IPC object is determined by OR'ing the following constants into the flag argument:

     S_IRUSR	   Read access for owner.

     S_IWUSR	   Write access for owner.

     S_IRGRP	   Read access for group.

     S_IWGRP	   Write access for group.

     S_IROTH	   Read access for other.

     S_IWOTH	   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 identifier 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 previously existing segment.  Size specified is less than the system
			imposed minimum, or greater than the system imposed 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 satisfy the request.

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

SEE ALSO

     shmat(2), shmctl(2), shmdt(2), stat(2), ftok(3)

BSD
								 December 17, 2010							       BSD

shmget(2)							System Calls Manual							 shmget(2)

Name
       shmget - get shared memory segment

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

       int shmget (key, size, shmflg)
       key_t key;
       int size, shmflg;

Description
       The system call returns the shared memory identifier associated with key.

       A  shared  memory  identifier and associated data structure and shared memory segment of size size bytes are created for key, if one of the
       following is true:

	    The key is equal to IPC_PRIVATE.  For further information, see

	    The key does not already have a shared memory identifier associated with it, and (shmflg & IPC_CREAT ) is true.

       Upon creation, the data structure associated with the new shared memory identifier is initialized as follows:

	    The and are set equal to the effective user ID and effective group ID of the calling process.

	    The low-order nine bits of are set equal to the low-order nine bits of shmflg.  The is set equal to the value of size.

	    The and are set equal to zero (0).	The shm_ctime is set equal to the current time.

Return Values
       Upon successful completion, a non-negative integer, namely, a shared memory identifier is returned.  Otherwise, a value of -1  is  returned
       and errno is set to indicated the error.

Diagnostics
       The system call fails if any of the following is true:

       [EINVAL]       The size is less than the system-imposed minimum or greater than the system-imposed maximum.

       [EACCES]       A  shared  memory  identifier  exists for key, but operations permission, as specified by the low-order nine bits of shmflg,
		      would not be granted.  For further information, see

       [EINVAL]       A shared memory identifier exists for key, but the size of the segment associated with it is less than size and size is  not
		      equal to zero.

       [ENOENT]       A shared memory identifier does not exist for key, and (shmflg & IPC_CREAT ) is false.

       [ENOSPC]       A  shared  memory  identifier  is to be created, but the system-imposed limit on the maximum number of allowed shared memory
		      identifiers would be exceeded.

       [ENOMEM]       A shared memory identifier and the associated shared memory segment are to be created, but the amount of available  physical
		      memory is not sufficient to fill the request.

       [EEXIST]       A shared memory identifier exists for key, but ((shmflg & IPC_CREAT ) and (shmflg & IPC_EXCL )) is true.

See Also
       shmctl(2), shmop(2), ftok(3)

																	 shmget(2)