int ioctl(int fd, unsigned long
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 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
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.
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() system 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_console(2), ioctl_fat(2),
ioctl_getfsmap(2), ioctl_iflags(2), ioctl_list(2),
ioctl_ns(2), ioctl_tty(2), ioctl_userfaultfd(2),
open(2), sd(4), tty(4)
This page is part of release 5.01 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 https://www.kernel.org/doc/man-pages/.
- fd is not a valid file descriptor.
- argp references an inaccessible memory area.
- request or argp is not valid.
- fd is not associated with a character special device.
- The specified request does not apply to the kind of object that the file
descriptor fd references.