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ioctl - control device
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 d must be an open file descriptor.
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>.
If an error has occurred, a value of -1 is returned and errno is set to indicate the error.
Ioctl() will fail if:
An ioctl() function call appeared in Version 7 AT&T UNIX.