---
name: "ftok"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/ftok"
---

# ftok(3)

create IPC identifier from path name

## NAME

**ftok** – create IPC identifier from path name

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/ipc.h\>**

*key\_t*\

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

## DESCRIPTION

The **ftok**() function attempts to create a unique key suitable for use with the [semget(2)](/semget/2.md), and [shmget(2)](/shmget/2.md) 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*.

## RETURN VALUES

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

## LEGACY SYNOPSIS

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

The include file ⟨sys/types.h⟩ is necessary.

## SEE ALSO

[semget(2)](/semget/2.md), [shmget(2)](/shmget/2.md), [compat(5)](/compat/5.md)

## HISTORY

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

## AUTHORS

Thorsten Lockert ⟨*tholo@sigmasoft.com*⟩

## BUGS

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.