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

       ioctl - control device

       #include <sys/ioctl.h>

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

       The ioctl() function manipulates the underlying device parameters of special 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
       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 <sys/ioctl.h>.

       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.

       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 descrip-
              tor d references.

       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

       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.

       execve(2), fcntl(2), ioctl_list(2), open(2), sd(4), tty(4)

       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.ker-

Linux                             2000-09-21                          IOCTL(2)

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