FTOK(3) Library Functions Manual FTOK(3)

ftokcreate IPC identifier from path name

Standard C Library (libc, -lc)

#include <sys/ipc.h>

key_t
ftok(const char *path, int id);

The () function attempts to create a unique key suitable for use with the 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.

The ftok() function will return -1 if path does not exist or if it cannot be accessed by the calling process.

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

The include file <sys/types.h> is necessary.

semget(2), shmget(2), compat(5)

The ftok() function originates with System V and is typically used by programs that use the System V IPC routines.

Thorsten Lockert ⟨tholo@sigmasoft.com⟩

The returned key is computed based on the device minor number and inode of the specified path, in combination with the lower 8 bits of the given id. Thus, it is quite possible for the routine to return duplicate keys.

July 9, 2009 macOS 15.0