IOCTL

ioctl ? control device

#include <sys/ioctl.h>

int ioctl(int d, int request, ...)

[The "third" argument is traditionally char *argp, and will be so named for this discussion.]

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 d 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>.

On success, zero is returned. On error, ?1 is returned, and errno is set appropriately.

EBADF

d is not a valid descriptor.

EFAULT

argp references an inaccessible memory area.

ENOTTY

d is not associated with a character special device.

ENOTTY

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

EINVAL

Request or argp is not valid.

No single standard. Arguments, returns, and semantics of ioctl(2) vary according to the device driver in question (the call is used as a catch-all for operations that don’t cleanly fit the Unix stream I/O model). See ioctl_list(2) for a list of many of the known ioctl calls. The ioctl function call appeared in Version 7 AT&T Unix.

execve(2), fcntl(2), mt(4), sd(4), tty(4)