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ioctl(2) System Calls Manual ioctl(2) NAME ioctl - Controls devices SYNOPSIS #include <stropts.h> int ioctl( int fildes, int request, ... /* arg */); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: ioctl(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS 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() re- quest and device to which the ioctl is targeted. See the appropriate Section 7 reference page or the documentation accompanying the device for more information. DESCRIPTION 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 para- meters are passed to the file designated by fildes and are interpreted 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 lo- cated 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). RETURN VALUES 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 indi- cate the error. ERRORS The ioctl() function sets errno to the specified values for the follow- ing 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. [XPG4-UNIX] The fildes parameter is not associated with a STREAMS device that accepts control functions. [Digital] 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 de- vice driver does not support the ioctl() function. RELATED INFORMATION Functions: exec(2), fcntl(2) Files: tty(7), lvm(7), streamio(7) Standards: standards(5) delim off ioctl(2)