IOCTL(2) manual page
Table of Contents
ioctl - control device
#include
<sys/ioctl.h>
int ioctl(int fd, unsigned long request, ...);
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
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>.
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.
- EBADF
- fd is not a valid 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 descriptor
fd references.
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.
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.
execve(2)
, fcntl(2)
, ioctl_list(2)
, open(2)
,
sd(4)
, tty(4)
This page is part of release 3.78 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 http://www.kernel.org/doc/man-pages/.
Table of Contents
![[Go to CFHT Home Page]](/images/cfht-icon.gif){kind=icon}
Man Pages 
Back to Software Index 
Manpage Top Level