ioctl(2) System Calls Manual ioctl(2)
ioctl - Controls devices
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Interfaces documented on this reference page conform to industry standards as follows:
Refer to the standards(5) reference page for more information about industry standards and associated tags.
Specifies the file descriptor of the requested device. Specifies the ioctl command to be performed on the device. Specifies parameters
for this request. The type of arg is dependent on the specific ioctl() request and device to which the ioctl is targeted. See the appro-
priate Section 7 reference page or the documentation accompanying the device for more information.
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 and arg parameters are passed to the file designated by fildes and are inter-
preted by the device driver. This control is occasionally used on non-STREAMS devices, with the basic input/output functions performed
through the read() and write() system calls.
An ioctl() request has encoded in it whether the parameter is an "in" parameter or "out" parameter, and the size of the arg parameter in
bytes. Macros and defines used to specify an ioctl() request are located in the <stropts.h> header file.
For STREAMS files, specific functions are performed by the ioctl() function as described in streamio(7).
STREAMS errors are described in streamio(7).
Upon successful completion, the ioctl() function returns a value other than -1 that depends upon the STREAMS device control function.
If an error occurs, a value of -1 is returned and errno is set to indicate the error.
The ioctl() function sets errno to the specified values for the following general conditions: The fildes parameter is not a valid open file
descriptor. A signal was caught during the ioctl() operation. The STREAM or multiplexer referenced by fildes is linked (directly or indi-
rectly) downstream from a multiplexer.
If an underlying device driver detects an error, errno may be set to one of the following values: Either the request or arg parameter is
not valid. Some physical I/O error has occurred. The fildes parameter is not associated with a STREAMS device that accepts control func-
tions. (Defined for Issue 4 Version 2 and higher issues of the XSH specification.) [Tru64 UNIX] The fildes parameter is not associated
with a character special device, or the specified request does not apply to the kind of object that the fildes parameter references. The
request and arg parameters are valid for this device driver, but the service requested cannot be performed on the particular subdevice.
The fildes parameter refers to a valid STREAMS device, but the corresponding device driver does not support the ioctl() function.
Functions: exec(2), fcntl(2)
Files: tty(7), streamio(7)
Standards: standards(5) delim off