IOCTL(2) - man page online | system calls

Control device.

IOCTL(2)                            Linux Programmer's Manual                            IOCTL(2)

NAME ioctl - control device
SYNOPSIS #include <sys/ioctl.h> int ioctl(int fd, unsigned long request, ...);
DESCRIPTION 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 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 paramÔÇÉ eter, 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>.
RETURN VALUE 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.
ERRORS EBADF fd is not a valid descriptor. EFAULT argp references an inaccessible memory area. EINVAL request or argp is not valid. ENOTTY fd is not associated with a character special device. ENOTTY The specified request does not apply to the kind of object that the descriptor fd references.
CONFORMING TO 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() function call appeared in Version 7 AT&T UNIX.
NOTES 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.
SEE ALSO execve(2), fcntl(2), ioctl_fat(2), ioctl_list(2), open(2), console_ioctl(4), tty_ioctl(4), sd(4), tty(4)
COLOPHON This page is part of release 4.04 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
Linux 2015-05-07 IOCTL(2)
This manual Reference Other manuals
ioctl(2) referred by aac(4freebsd) | aacraid(4freebsd) | agp(4freebsd) | agpgart(4freebsd) | apple2(6x) | apropos(1) | arp(7) | aufs(5) | bnchat(1) | bpf(4freebsd) | cap_ioctls_get(2freebsd) | cap_ioctls_limit(2freebsd) | capabilities(7) | carp(4freebsd) | cd(4freebsd) | ch(4freebsd) | collectd.conf(5) | console_ioctl(4) | cpuctl(4freebsd) | crypto(4freebsd)
refer to console_ioctl(4) | execve(2) | fcntl(2) | ioctl_fat(2) | ioctl_list(2) | open(2) | sd(4) | tty(4) | tty_ioctl(4)