ioctl - control device


   #include <sys/ioctl.h>

   int ioctl(int fd, 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 fd 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 nonnegative value on
   success.  On error, -1 is returned, and errno is set appropriately.


   EBADF  fd is not a valid file descriptor.

   EFAULT argp references an inaccessible memory area.

   EINVAL request or argp is not valid.

   ENOTTY fd is not associated with a character special device.

   ENOTTY The specified request does not apply to the kind of object  that
          the file descriptor fd 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_fat(2),     ioctl_ficlonerange(2),
   ioctl_fideduperange(2),   ioctl_list(2),   open(2),   console_ioctl(4),
   sd(4), tty(4), tty_ioctl(4)


   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at


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