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.\"     @(#)ioctl.2	8.2 (Berkeley) 12/11/93
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.TH IOCTL 2 "16 January 1997" GNO "System Calls"
.SH NAME
.BR ioctl
\- control device
.SH SYNOPSIS
.br
#include <sys/ioctl.h>
.sp 1
int
\fBioctl\fR (int \fId\fR, unsigned long \fIrequest\fR, void *\fIargp\fR);
.SH DESCRIPTION
The
.BR 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
.BR ioctl 
requests.
The argument
.I d
must be an open file descriptor.
.LP
An  ioctl
.I request
has encoded in it whether the argument is an 'in'
parameter or 'out'
parameter, and the size of the argument
.I argp
in bytes.
Macros and defines used in specifying an ioctl
.I request
are located in the file <sys/ioctl.h>.
.LP
The writeups of various devices in chapter 4 discuss how 
.BR ioctl
applies to them.
.SH RETURN VALUES
If an error has occurred, a value of -1 is returned and
.IR errno
is set to indicate the error.
.SH ERRORS
.BR Ioctl 
will fail if:
.RS
.IP \fBEBADF\fR
.I d
is not a valid descriptor.
.IP \fBENOTTY\fR
.I d
is not associated with a character
special device.
.IP \fBENOTTY\fR
The specified request does not apply to the kind
of object that the descriptor
.I d
references.
.IP \fBEINVAL\fR
.I Request
or
.I argp
is not valid.
.RE
.SH SEE ALSO
.BR mt (1),
.BR execve (2),
.BR fcntl (2),
.BR tty (4),
.BR intro (4)
.SH HISTORY
An
.BR ioctl
function call appeared in Version 7 AT&T UNIX.