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ioctl - control device
Standard C Library (libc, -lc)
ioctl(int d, unsigned long request, ...);
The ioctl() 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 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
If an error has occurred, a value of -1 is returned and errno is set to
indicate the error.
The ioctl() system call will fail if:
[EBADF] The d argument is not a valid descriptor.
[ENOTTY] The d argument is not associated with a character
[ENOTTY] The specified request does not apply to the kind of
object that the descriptor d references.
[EINVAL] The request or argp argument is not valid.
[EFAULT] The argp argument points outside the process’s
allocated address space.
execve(2), fcntl(2), intro(4), tty(4)
The ioctl() function appeared in Version 7 AT&T UNIX.