ioctl(2)

1IOCTL(2)                   Linux Programmer's Manual                  IOCTL(2)
2
3
4

NAME

6       ioctl - control device
7

SYNOPSIS

9       #include <sys/ioctl.h>
10
11       int ioctl(int d, int request, ...);
12

DESCRIPTION

14       The  ioctl()  function  manipulates the underlying device parameters of
15       special files.  In particular, many operating characteristics of  char‐
16       acter  special  files  (e.g.  terminals) may be controlled with ioctl()
17       requests.  The argument d must be an open file descriptor.
18
19       The second argument is a  device-dependent  request  code.   The  third
20       argument  is  an  untyped  pointer  to memory.  It's traditionally char
21       *argp (from the days before void * was valid C), and will be  so  named
22       for this discussion.
23
24       An  ioctl()  request  has  encoded  in it whether the argument is an in
25       parameter or out parameter, and the size of the argument argp in bytes.
26       Macros and defines used in specifying an ioctl() request are located in
27       the file <sys/ioctl.h>.
28

RETURN VALUE

30       Usually, on success zero is returned.  A few ioctl() requests  use  the
31       return  value  as an output parameter and return a nonnegative value on
32       success.  On error, -1 is returned, and errno is set appropriately.
33

ERRORS

35       EBADF  d is not a valid descriptor.
36
37       EFAULT argp references an inaccessible memory area.
38
39       EINVAL Request or argp is not valid.
40
41       ENOTTY d is not associated with a character special device.
42
43       ENOTTY The specified request does not apply to the kind of object  that
44              the descriptor d references.
45

NOTE

47       In  order  to  use this call, one needs an open file descriptor.  Often
48       the open(2) call has unwanted side effects, that can be  avoided  under
49       Linux by giving it the O_NONBLOCK flag.
50

CONFORMING TO

52       No single standard.  Arguments, returns, and semantics of ioctl(2) vary
53       according to the device driver in question  (the  call  is  used  as  a
54       catch-all  for  operations  that  don't cleanly fit the Unix stream I/O
55       model).  See ioctl_list(2) for a list of  many  of  the  known  ioctl()
56       calls.  The ioctl() function call appeared in Version 7 AT&T Unix.
57