IOCTL(S) UNIX System V IOCTL(S)
Name
ioctl - control device
Syntax
int ioctl (fildes, request, arg)
int fildes, request;
Description
The ioctl system call performs a variety of control
functions on devices and STREAMS. For non-STREAMS files,
the functions performed by this call are device-specific
control functions. The arguments request and arg are passed
to the file designated by fildes and are interpreted by the
device driver. This control is infrequently used on non-
STREAMS devices, with the basic input/output functions
performed through the read(S) and write(S) system calls.
fildes is an open file descriptor that refers to a device.
request selects the control function to be performed and
will depend on the device being addressed. arg represents
additional information that is needed by this specific
device to perform the requested function. The data type of
arg depends upon the particular control request, but it is
either an integer or a pointer to a device-specific data
structure.
In addition to device-specific and STREAMS functions,
generic functions are provided by more than one device
driver, for example, the general terminal interface (see
termio(M)).
The ioctl system call will fail for any type of file if one
or more of the following is true:
[EBADF] fildes is not a valid open file descriptor.
[ENOTTY] fildes is not associated with a device driver
that accepts control functions.
[EINTR] A signal was caught during the ioctl system
call.
The ioctl system call will also fail if the device driver
detects an error. In this case, the error is passed through
ioctl without change to the caller. A particular driver
might not have all of the following error cases. Other
requests to device drivers will fail if one or more of the
following is true:
[EFAULT] Request requires a data transfer to or from a
buffer pointed to by arg, but some part of
the buffer is outside the process's allocated
space.
[EINVAL] Request or arg is not valid for this device.
[EIO] Some physical I/O error has occurred.
[ENXIO] The request and arg are valid for this device
driver, but the service requested cannot be
performed on this particular subdevice.
[ENOLINK] Fildes is on a remote machine and the link to
that machine is no longer active.
STREAMS errors are described in streamio(7).
See Also
termio(M)
Diagnostics
Upon successful completion, the value returned depends upon
the device control function, but must be a non-negative
integer. Otherwise, a value of -1 is returned, and errno is
set to indicate the error.
Standards Conformance
ioctl is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
and The X/Open Portability Guide II of January 1987.
(printed 6/20/89)