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RedHat 9 (Linux i386) - man page for ftok (redhat section 3)

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 char-
       acter 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)


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