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ioctl(2) - ioctl, ioctl - control device - man 2 ioctl

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



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 spe-
       cial 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(2,3,n) file(1,n) 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(5,8)
       for this discussion.

       An ioctl request has encoded in(1,8) it whether the argument is an in(1,8) param-
       eter or out parameter, and the size of  the  argument  argp  in(1,8)  bytes.
       Macros  and  defines used in(1,8) specifying an ioctl request are located in(1,8)
       the file(1,n) <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(8,n), -1 is returned, and errno is set(7,n,1 builtins) 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.

NOTE
       In  order  to  use this call, one needs an open(2,3,n) file(1,n) descriptor.  Often
       the open(2,3,n)(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(1,8) 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(1,8) Version 7 AT&T Unix.

SEE ALSO
       execve(2), fcntl(2), ioctl_list(2), open(2,3,n)(2), mt(4), sd(4), tty(1,4)(4)



BSD Man Page                      2000-09-21                          IOCTL(2)

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