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.\"     @(#)ioctl.2	8.2 (Berkeley) 12/11/93
.\"
.\" $FreeBSD$
.\"
.Dd December 11, 1993
.Dt IOCTL 2
.Os
.Sh NAME
.Nm ioctl
.Nd control device
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/ioctl.h
.Ft int
.Fn ioctl "int d" "unsigned long request" ...
.Sh DESCRIPTION
The
.Fn 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
.Fn ioctl
requests.
The argument
.Fa d
must be an open file descriptor.
.Pp
The third argument to
.Fn ioctl
is traditionally named
.Va "char *argp" .
Most uses of
.Fn ioctl
in
.Fx 3.0 ,
however, require the third argument to be a
.Vt caddr_t
or an
.Vt int .
.Pp
An
.Fn ioctl
.Fa request
has encoded in it whether the argument is an
.Dq in
argument
or
.Dq out
argument, and the size of the argument
.Fa argp
in bytes.
Macros and defines used in specifying an ioctl
.Fa request
are located in the file
.In sys/ioctl.h .
.Sh RETURN VALUES
If an error has occurred, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn ioctl
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa d
argument
is not a valid descriptor.
.It Bq Er ENOTTY
The
.Fa d
argument
is not associated with a character
special device.
.It Bq Er ENOTTY
The specified request does not apply to the kind
of object that the descriptor
.Fa d
references.
.It Bq Er EINVAL
The
.Fa request
or
.Fa argp
argument
is not valid.
.It Bq Er EFAULT
The
.Fa argp
argument
points outside the process's allocated address space.
.El
.Sh SEE ALSO
.Xr execve 2 ,
.Xr fcntl 2 ,
.Xr intro 4 ,
.Xr tty 4
.Sh HISTORY
The
.Fn ioctl
function appeared in
.At v7 .