ioctl(2) -- Linux man page
NAME
ioctl - control device
SYNOPSIS
#include <sys/ioctl.h>
int ioctl(int d, int request, ...);
DESCRIPTION
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 ioctls use the return value as an output parameter
and return a nonnegative 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.
- 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.
- EINVAL
-
Request
or
argp
is not valid.
NOTE
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.
CONFORMING TO
No single standard. Arguments, returns, and semantics of
ioctl(2)
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.
SEE ALSO
execve(2),
fcntl(2),
ioctl_list(2),
open(2),
mt(4),
sd(4),
tty(4)
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