ioctl - control device
int ioctl(int fildes, int request, /* arg */ ...);
The ioctl() function performs a variety of control functions
on devices and STREAMS. For non-STREAMS files, the functions
performed by this call are device-specific control func-
The request argument and an optional third argument with
varying type are passed to the file designated by fildes and
are interpreted by the device driver.
For STREAMS files, specific functions are performed by the
ioctl() function as described in streamio(7I).
The fildes argument is an open file descriptor that refers
to a device. The request argument selects the control func-
tion to be performed and depends on the device being
addressed. The arg argument represents a third argument
that has 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 int or a pointer to a device-specific data
In addition to device-specific and STREAMS functions, gen-
eric functions are provided by more than one device driver
(for example, the general terminal interface.) See
Upon successful completion, the value returned depends upon
the device control function, but must be a non-negative
integer. Otherwise, -1 is returned and errno is set to
indicate the error.
The ioctl() function will fail for any type of file if:
EBADF The fildes argument is not a valid open file descrip-
EINTR A signal was caught during the execution of the
The STREAM or multiplexer referenced by fildes is
linked (directly or indirectly) downstream from a mul-
The ioctl() function 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. Under the
following conditions, requests to device drivers may fail
and set errno to indicate the error
The request argument requires a data transfer to or
from a buffer pointed to by arg, but arg points to an
The request or arg argument is not valid for this dev-
EIO Some physical I/O error has occurred.
The fildes argument is on a remote machine and the
link to that machine is no longer active.
The fildes argument is not associated with a STREAMS
device that accepts control functions.
ENXIO The request and arg arguments are valid for this dev-
ice driver, but the service requested can not be per-
formed on this particular subdevice.
The fildes argument refers to a valid STREAMS device,
but the corresponding device driver does not support
the ioctl() function.
STREAMS errors are described in streamio(7I).
Man(1) output converted with