MirBSD manpage: ioctl(2)

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


     ioctl - control device


     #include <sys/ioctl.h>

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


     The ioctl() function manipulates the underlying device parameters of spe-
     cial 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 third argument is
     called arg and contains additional information needed by this device to
     perform the requested function. arg is either an int or a pointer to a
     device-specific data structure, depending upon the given request.

     An ioctl request has encoded in it whether the argument is an "in" param-
     eter or "out" parameter, and the size of the third argument (arg) in
     bytes. Macros and defines used in specifying an ioctl request are located
     in the file <sys/ioctl.h>.


     Some ioctls are applicable to any file descriptor. These include:

             Set close-on-exec flag. The file will be closed when exec(3) is

             Clear close-on-exec flag. The file will remain open across

     Some generic ioctls are not implemented for all types of file descrip-
     tors. These include:

     FIONREAD int
             Get the number of bytes that are immediately available for read-

     FIONBIO int
             Set non-blocking I/O mode if the argument is non-zero. In non-
             blocking mode, read(2) or write(2) calls return -1 and set errno
             to EAGAIN immediately when no data is available.

     FIONASYNC int
             Set asynchronous I/O mode if the argument is non-zero. In asyn-
             chronous mode, the process or process group specified by
             FIOSETOWN will start receiving SIGIO signals when data is avail-
             able. The SIGIO signal will be delivered when data is available
             on the file descriptor.

             Set/get the process or the process group (if negative) that
             should receive SIGIO signals when data is available.


     If an error has occurred, a value of -1 is returned and errno is set to
     indicate the error.


     ioctl() will fail if:

     [EBADF]       d is not a valid descriptor.

     [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.

     [EINVAL]      request or arg is not valid.

     [EFAULT]      arg points outside the process's allocated address space.


     cdio(1), chio(1), mt(1), execve(2), fcntl(2), intro(4), tty(4)


     An ioctl() function call appeared in Version 7 AT&T UNIX.

MirBSD #10-current            December 11, 1993                              1

Generated on 2021-12-07 11:07:08 by $MirOS: src/scripts/roff2htm,v 1.103 2021/01/23 20:24:35 tg Exp $ — This product includes material provided by mirabilos.

These manual pages and other documentation are copyrighted by their respective writers; their sources are available at the project’s CVSweb, AnonCVS and other mirrors. The rest is Copyright © 2002–2021 MirBSD.

This manual page’s HTML representation is supposed to be valid XHTML/1.1; if not, please send a bug report — diffs preferred.