Modification of the mo virtual printer attribute

All virtual printer definitions contain an attribute named mo.

The mo attribute specifies the command string to invoke the device driver interface program. The device driver interface program is the last process in the input data stream processing pipeline and, in the case of local spooler queues with piobe as the backend, is usually pioout. It is named the device driver interface program because, as the last process in the pipeline, it generally opens the device driver for writing and then writes the processed input data stream to the device driver. See Datastream flow for common print jobs for additional information.

The design of the base operating system spooler allows the root user to replace the pieces of the input data stream of the processing pipeline with user-written code. An example of redefining the mo attribute, whose default value is the full path of pioout, to the full path of a user-written delivery program is covered. See Backend processing for more information.