ioctl - control device
#include <sys/ioctl.h>
int ioctl(int fd
, 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 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 <sys/ioctl.h>
.
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.
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.
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_ficlonerange(2), ioctl_fideduperange(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 4.15 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/.