ioctl - control device
ioctl(int d, unsigned long request, ...);
The ioctl() function manipulates the underlying device parameters of special
files. In particular, many operating characteristics
special files (e.g., terminals) may be controlled with
The argument d must be an open file descriptor. The third
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
An ioctl request has encoded in it whether the argument is
an ``in'' parameter
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
Set close-on-exec flag. The file will be closed
when exec(3) is
Clear close-on-exec flag. The file will remain open
Some generic ioctls are not implemented for all types of
Get the number of bytes that are immediately available for reading.
Set non-blocking I/O mode if the argument is non-zero. In nonblocking
mode, read(2) or write(2) calls return -1
and set errno
to EAGAIN immediately when no data is available.
Set asynchronous I/O mode if the argument is non-zero. In asynchronous
mode, the process or process group specified by
FIOSETOWN will start receiving SIGIO signals when
data is available.
The SIGIO signal will be delivered when data
on the file descriptor.
FIOSETOWN, FIOGETOWN int
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
[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),
An ioctl() function call appeared in Version 7 AT&T UNIX.
OpenBSD 3.6 December 11, 1993
[ Back ]