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.
The second argument is a device-dependent request code.
The third argument is an untyped pointer to memory.
It's traditionally
char *argp
(from the days before
void *
was valid C), and will be so named for this discussion.
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
ioctl()
requests use the return value as an output parameter
and return a non-negative 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.
EINVAL
Request
or
argp
is not valid.
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.
CONFORMING TO
No single standard.
Arguments, returns, and semantics of
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
ioctl_list(2)
for a list of many of the known
ioctl()
calls.
The
ioctl()
function call appeared in Version 7 AT&T Unix.
NOTES
In order to use this call, one needs an open file descriptor.
Often the
open(2)
call has unwanted side effects, that can be avoided under Linux
by giving it the
O_NONBLOCK
flag.
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
