ioctl – control device


       ioctl - control device



       int ioctl(int d, unsigned long 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 .


       Usually, on success zero is returned.  A few ioctl() requests use the
       return value as an output parameter and return a nonnegative 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 descriptor 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 UNIX.


       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 3.55 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at

Linux                            2013-11-08                         IOCTL(2)