IOCTL
Section: Linux Programmer's Manual (2)
Updated: 2017-05-03
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NAME
ioctl - control device
SYNOPSIS
#include <sys/ioctl.h>
int ioctl(int fd, unsigned long 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
fd
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 nonnegative value on success.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- EBADF
-
fd
is not a valid file descriptor.
- EFAULT
-
argp
references an inaccessible memory area.
- EINVAL
-
request
or
argp
is not valid.
- ENOTTY
-
fd
is not associated with a character special device.
- ENOTTY
-
The specified request does not apply to the kind of object that the
file descriptor
fd
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.
SEE ALSO
execve(2),
fcntl(2),
ioctl_console(2),
ioctl_fat(2),
ioctl_ficlonerange(2),
ioctl_fideduperange(2),
ioctl_getfsmap(2),
ioctl_iflags(2),
ioctl_list(2),
ioctl_ns(2),
ioctl_tty(2),
ioctl_userfaultfd(2),
open(2),
sd(4),
tty(4)
COLOPHON
This page is part of release 4.13 of the Linux
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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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