documents: ioctl
IOCTL(2) System Calls Manual IOCTL(2)

ioctl — control device

#include <sys/ioctl.h>

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

The () 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⟩.

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

ioctl() will fail if:

[]
fildes is not a valid descriptor.
[]
Request or argp is not valid.
[]
fildes is not associated with a character special device.
[]
The specified request does not apply to the kind of object that the descriptor fildes references.

cdio(1), chio(1), mt(1), execve(2), fcntl(2), intro(4), tty(4)

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

December 11, 1993 BSD 4