Hanging d.mon -L

Can someone please give me a run-down on the information provided by d.mon -L?
It gives monitor status as 'running', not running', 'in use', and '??'. The
first 2 categories are straightforward, but the last 2 I am having difficulty
in fathoming. Worse, the command occasionally hangs and freezes up the
keyboard, even when all monitors look to be OK. Can anybody give me a clue
about what is going on? Release 4.0, nb, with Sparcs as X terminals.

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Conn V Copas
Loughborough University of Technology tel : +44 (0)509 222689
Computer-Human Interaction Research Centre fax : +44 (0)509 610815
Leicestershire LE11 3TU e-mail - (Janet):C.V.Copas@uk.ac.lut
G Britain (Internet):C.V.Copas@lut.ac.uk