NAME
ioctl —
control device
LIBRARY
library “libc”
SYNOPSIS
#include
<sys/ioctl.h>
int
ioctl(int
d, unsigned long
request, ...);
DESCRIPTION
Theioctl()
system call 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 third argument to
ioctl() is
traditionally named char *argp. Most uses of
ioctl() however, require the third argument to be a
caddr_t or an int.
An
ioctl()
request has encoded in it whether the argument is an
“in” argument or “out” argument, 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 VALUES
If an error has occurred, a value of -1 is returned and errno is set to indicate the error.
ERRORS
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 argp is not valid.
- [
EFAULT] - argp points outside the process's allocated address space.
SEE ALSO
HISTORY
An ioctl() function call appeared in
Version 7 AT&T UNIX.