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

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

NAME         top

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

SYNOPSIS         top

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

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

DESCRIPTION         top

       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         top

       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.

ATTRIBUTES         top

   Multithreading (see pthreads(7))
       The ftok() function is thread-safe.

CONFORMING TO         top

       POSIX.1-2001.

NOTES         top

       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 behavior 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 inode 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         top

       msgget(2), semget(2), shmget(2), stat(2), svipc(7)

COLOPHON         top

       This page is part of release 3.70 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       http://www.kernel.org/doc/man-pages/.

GNU                              2013-10-07                          FTOK(3)