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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 special files.  In particular, many oper-
       ating characteristics of character 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  discus-
       sion.

       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 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  ques-
       tion  (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  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2000-09-21                          IOCTL(2)