The API does provide some limited debugging facilities which can help in tracking down unusual behavior. The routine PMDFdebug can be called to enable debugging output for either enqueuing or dequeuing operations. On OpenVMS systems, all debugging output is written to PMDF_OUTPUT if defined or to SYS$OUTPUT otherwise. On UNIX and Windows systems, debugging output is written to stdout.

PMDFdebug should be called after either PMDFenqueueInitialize or PMDFdequeueInitialize or both have been called.

Further debugging output can be enabled by setting OS_DEBUG=1 in the PMDF option file.

Message enqueue and dequeue activities performed through the PMDF API (and callable SEND) will be logged when the channels involved are marked with the logging channel keyword.