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FTOK(3)			   Linux Programmer's Manual		       FTOK(3)

NAME
       ftok  -	convert	 a pathname and	a project identifier to	a System V IPC
       key

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

       key_t ftok(const	char *pathname,	int proj_id);

DESCRIPTION
       The ftok	function uses the identity of the  file	 named	by  the	 given
       pathname	 (which	 must  refer  to an existing, accessible file) and the
       least significant 8 bits	of proj_id (which must be nonzero) to generate
       a  key_t	 type  System  V  IPC  key,  suitable  for use with msgget(2),
       semget(2), or shmget(2).

       The resulting value is the same for all pathnames that  name  the  same
       file, when the same value of proj_id is used. The value returned	should
       be different when the (simultaneously existing) files  or  the  project
       IDs differ.

RETURN VALUE
       On  success  the	 generated  key_t  value is returned. On failure -1 is
       returned, with errno indicating the error as  for  the  stat(2)	system
       call.

CONFORMING TO
       XPG4

NOTES
       Under libc4 and libc5 (and under	SunOS 4.x) the prototype was
	      key_t ftok(char *pathname, char proj_id);
       Today  proj_id is an int, but still only	8 bits are used. Typical usage
       has an ASCII character proj_id, that is why the behaviour is said to be
       undefined when proj_id is zero.

       Of course no guarantee can be given that	the resulting key_t is unique.
       Typically, a best effort	attempt	combines the given proj_id  byte,  the
       lower  16 bits of the i-node number, and	the lower 8 bits of the	device
       number into a 32-bit result.  Collisions	may easily happen, for example
       between files on	/dev/hda1 and files on /dev/sda1.

SEE ALSO
       ipc(5), msgget(2), semget(2), shmget(2),	stat(2)

Linux 2.4			  2001-11-28			       FTOK(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO

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