IOCTL(2)IOCTL(2)NAMEioctl - 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 functions. 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 function 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 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(7I)).
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:
The fildes argument is not a valid open file descriptor.
A signal was caught during the execution of the ioctl() func‐
The stream or multiplexer referenced by fildes is linked
(directly or indirectly) downstream from a multiplexer.
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 illegal
The request or arg argument is not valid for this device.
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that machine is no longer active.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.
The request and arg arguments are valid for this device
driver, but the service requested can not be performed on
this particular subdevice.
The fildes argument refers to a valid streams device, but
the corresponding device driver does not support the ioctl()
Streams errors are described in streamio(7I).
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Standard │
SEE ALSOattributes(5), standards(5), streamio(7I), termio(7I)
Feb 15, 1996 IOCTL(2)