---
name: "ioctl"
section: "2"
platform: "macos"
package: "xnu"
version: "12377.121.6"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/ioctl"
---

# ioctl(2)

control device

## NAME

**ioctl** – control device

## SYNOPSIS

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

*int*\

**ioctl**(*int fildes*, *unsigned long request*, *...*);

## DESCRIPTION

The **ioctl**() function manipulates the underlying device parameters of special files. In particular, many operating characteristics of character special files (e.g. terminals) may be controlled with **ioctl**() requests. The argument *fildes* must be an open file descriptor.

An  ioctl *request* has encoded in it whether the argument is an “in” parameter or “out” parameter, and the size of the argument *argp* in bytes. Macros and defines used in specifying an ioctl *request* are located in the file ⟨*sys/ioctl.h*⟩.

## RETURN VALUES

If an error has occurred, a value of -1 is returned and *errno* is set to indicate the error.

## ERRORS

**ioctl**() will fail if:

- \[EBADF\]

  *fildes* is not a valid descriptor.

- \[EINVAL\]

  *Request* or *argp* is not valid.

- \[ENOTTY\]

  *fildes* is not associated with a character special device.

- \[ENOTTY\]

  The specified request does not apply to the kind of object that the descriptor *fildes* references.

## SEE ALSO

[cdio(1)](/cdio/1.md), [chio(1)](/chio/1.md), [mt(1)](/mt/1.md), [execve(2)](/execve/2.md), [fcntl(2)](/fcntl/2.md), [intro(4)](/intro/4.md), [tty(4)](/tty/4.md)

## HISTORY

An **ioctl**() function call appeared in  Version 7 AT&T UNIX.