FTOK(3) Library Functions Manual FTOK(3)
ftok -- create IPC identifier from path name
Standard C Library (libc, -lc)
ftok(const char *path, int id);
The ftok() function attempts to create a unique key suitable for use with
the msgget(2), semget(2) and shmget(2) functions given the path of an
existing file and a user-selectable id.
The specified path must specify an existing file that is accessible to
the calling process or the call will fail. Also, note that links to
files will return the same key, given the same id.
Only the 8 least significant bits of id are used in the key generation;
the rest of the bits are ignored.
The ftok() function will return ((key_t)-1) if path does not exist or if
it cannot be accessed by the calling process.
msgget(2), semget(2), shmget(2)
The ftok() function conforms to IEEE Std 1003.1 (``POSIX.1'').
The ftok() function originated with System V and is typically used by
programs that use the System V IPC routines.
Thorsten Lockert <tholoATsigmasoft.com>
The returned key is computed based on the device and inode of the
specified path in combination with the given id. Thus it is quite
possible for the routine to return duplicate keys given that those fields
are not 8- and 16-bit quantities like they were on System V based systems
where this library routine's ancestor were originally created.
NetBSD 6.1.5 April 27, 2010 NetBSD 6.1.5