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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 4.16 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/.