Standard C Library (libc, -lc)

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 or an

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 #include <sys/ioctl.h>

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 special device.
• [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