1IOCTL(2)                   Linux Programmer's Manual                  IOCTL(2)
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NAME

6       ioctl - control device
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SYNOPSIS

9       #include <sys/ioctl.h>
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11       int ioctl(int fd, unsigned long request, ...);
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DESCRIPTION

14       The ioctl() system call 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 fd must be an open file descriptor.
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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.
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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>.
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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.
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ERRORS

35       EBADF  fd is not a valid file descriptor.
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37       EFAULT argp references an inaccessible memory area.
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39       EINVAL request or argp is not valid.
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41       ENOTTY fd is not associated with a character special device.
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43       ENOTTY The specified request does not apply to the kind of object  that
44              the file descriptor fd references.
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CONFORMING TO

47       No  single standard.  Arguments, returns, and semantics of ioctl() vary
48       according to the device driver in question  (the  call  is  used  as  a
49       catch-all  for  operations  that  don't cleanly fit the UNIX stream I/O
50       model).  See ioctl_list(2) for a list of  many  of  the  known  ioctl()
51       calls.  The ioctl() system call appeared in Version 7 AT&T UNIX.
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NOTES

54       In  order  to  use this call, one needs an open file descriptor.  Often
55       the open(2) call has unwanted side effects, that can be  avoided  under
56       Linux by giving it the O_NONBLOCK flag.
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SEE ALSO

59       execve(2),   fcntl(2),  ioctl_console(2),  ioctl_fat(2),  ioctl_ficlon‐
60       erange(2), ioctl_fideduperange(2), ioctl_getfsmap(2),  ioctl_iflags(2),
61       ioctl_list(2),    ioctl_ns(2),    ioctl_tty(2),   ioctl_userfaultfd(2),
62       open(2), sd(4), tty(4)
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COLOPHON

65       This page is part of release 5.04 of the Linux  man-pages  project.   A
66       description  of  the project, information about reporting bugs, and the
67       latest    version    of    this    page,    can     be     found     at
68       https://www.kernel.org/doc/man-pages/.
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72Linux                             2017-05-03                          IOCTL(2)
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