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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 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 param-
       eter, 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  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  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.

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 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information    about    reporting    bugs,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.



Linux                                       2000-09-21                                   IOCTL(2)

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