ultrix man page for ioctl

ioctl(2)							System Calls Manual							  ioctl(2)

Name
       ioctl - control device

Syntax
       #include <sys/ioctl.h>

       ioctl(d, request, argp)
       int d, request;
       char *argp;

Description
       The  call  performs  a  variety of functions on open descriptors.  In particular, many operating characteristics of character special files
       (for example, terminals) can be controlled with requests.  Certain requests operate on a number of device  types.  These  include  informa-
       tional  requests,  such	as and The descriptions of various devices in the Reference Pages, Section 4: Special Files discuss how applies to
       them. Also consult <sys/ioctl.h> for more information.

       An 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 request are located in the file <sys/ioctl.h>.

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

Diagnostics
       The call fails under the following conditions:

       [EBADF]	      The d is not a valid descriptor.

       [ENOTTY]       The d is not associated with a character special device.

       [ENOTTY]       The specified request does not apply to the kind of object which the descriptor d references.

       [EINVAL]       The request or argp is not valid.

       [EFAULT]       The argp points to memory that is not part of the process' address space.

See Also
       execve(2), fcntl(2), devio(4), intro(4n), mu(4), nbuf(4), tty(4)

																	  ioctl(2)