IOCTL

Section: Linux Programmer's Manual (2)
Updated: 1993-07-23
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NAME

ioctl - control device

SYNOPSIS

#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.]

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 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>.

RETURN VALUE

Usually, on success zero is returned. A few ioctls use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, and errno is set appropriately.

ERRORS

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.

CONFORMING TO

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.

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