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.\"     @(#)ioctl.2	6.4 (Berkeley) 3/10/91

.\"

.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>

.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>

.\" Modified 1999-06-25 by Rachael Munns <vashti@dream.org.uk>

.\" Modified 2000-09-21 by Andries Brouwer <aeb@cwi.nl>

.\"

.TH IOCTL 2 2017-05-03 "Linux" "Linux Programmer's Manual"

.SH NAME

ioctl \- control device

.SH SYNOPSIS

.B #include <sys/ioctl.h>

.PP

.BI "int ioctl(int " fd ", unsigned long " request ", ...);"

.\" POSIX says 'request' is int, but glibc has the above

.\" See https://bugzilla.kernel.org/show_bug.cgi?id=42705

.SH DESCRIPTION

The

.BR ioctl ()

system call manipulates the underlying device parameters of special files.

In particular, many operating characteristics of character special files

(e.g., terminals) may be controlled with

.BR ioctl ()

requests.

The argument

.I fd

must be an open file descriptor.

.PP

The second argument is a device-dependent request code.

The third argument is an untyped pointer to memory.

It's traditionally

.BI "char *" argp

(from the days before

.B "void *"

was valid C), and will be so named for this discussion.

.PP

An

.BR ioctl ()

.I request

has encoded in it whether the argument is an

.I in

parameter or

.I out

parameter, and the size of the argument

.I argp

in bytes.

Macros and defines used in specifying an

.BR ioctl ()

.I request

are located in the file

.IR <sys/ioctl.h> .

.SH RETURN VALUE

Usually, on success zero is returned.

A few

.BR ioctl ()

requests use the return value as an output parameter

and return a nonnegative value on success.

On error, \-1 is returned, and

.I errno

is set appropriately.

.SH ERRORS

.TP 0.7i

.B EBADF

.I fd

is not a valid file descriptor.

.TP

.B EFAULT

.I argp

references an inaccessible memory area.

.TP

.B EINVAL

.I request

or

.I argp

is not valid.

.TP

.B ENOTTY

.I fd

is not associated with a character special device.

.TP

.B ENOTTY

The specified request does not apply to the kind of object that the

file descriptor

.I fd

references.

.SH CONFORMING TO

No single standard.

Arguments, returns, and semantics of

.BR ioctl ()

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

.BR ioctl_list (2)

for a list of many of the known

.BR ioctl ()

calls.

The

.BR ioctl ()

system call appeared in Version 7 AT&T UNIX.

.SH NOTES

In order to use this call, one needs an open file descriptor.

Often the

.BR open (2)

call has unwanted side effects, that can be avoided under Linux

by giving it the

.B O_NONBLOCK

flag.

.SH SEE ALSO

.BR execve (2),

.BR fcntl (2),

.BR ioctl_console (2),

.BR ioctl_fat (2),

.BR ioctl_ficlonerange (2),

.BR ioctl_fideduperange (2),

.BR ioctl_getfsmap (2),

.BR ioctl_iflags (2),

.BR ioctl_list (2),

.BR ioctl_ns (2),

.BR ioctl_tty (2),

.BR ioctl_userfaultfd (2),

.BR open (2),

.\" .BR mt (4),

.BR sd (4),

.BR tty (4)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.