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



NAME
       ioctl - control device

SYNOPSIS
       #include 

       int ioctl(int d, int request, ...);

DESCRIPTION
       The  ioctl()  function  manipulates the underlying device parameters of
       special files.  In particular, many operating characteristics of	 char-
       acter  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 .

RETURN VALUE
       Usually, on success zero is returned.  A few ioctl() requests  use  the
       return  value as an output parameter and return a non-negative 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.

       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.

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_list(2), open(2), sd(4), tty(4)

COLOPHON
       This  page  is  part of release 3.22 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux				  2000-09-21			      IOCTL(2)