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

NAME

     ioctl - control device

SYNOPSIS

     #include <sys/ioctl.h>

     int ioctl(int fd, unsigned long request, ...);

DESCRIPTION

     The ioctl() system call 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 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>.

RETURN VALUE

     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.

ERRORS

     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.

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() system 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_console(2),  ioctl_fat(2),  ioctl_ficlon-
     erange(2), ioctl_fideduperange(2), ioctl_getfsmap(2),  ioctl_iflags(2),
     ioctl_list(2),    ioctl_ns(2),    ioctl_tty(2),   ioctl_userfaultfd(2),
     open(2), sd(4), tty(4)

COLOPHON

     This page is part of release 4.16 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
     https://www.kernel.org/doc/man-pages/.

Linux 2017-05-03 IOCTL(2)