BSD Unix machines hanging

[Stephen J. Hartley]

> We have been experiencing a rather odd and intermittant problem with
> our Unix machines. It is not confined to a particular machine or Unix;
> Symptoms: The machines appear to lock up, users cannot get characters
> echoed, console is hung. In short, the machine seems dead. The only
> way to recover is a reboot. 

We have experienced the same problem with our VAX-11/750 and 780, each
running vanilla 4.3 BSD.  Same symptoms:  characters not echoed, console
dead.  We can only reboot to remove the problem.  However, this has only
happened in the last two months, since we brought up 4.3.  It never
happened that I can remember in the 2 1/2 years we ran 4.2 on these
machines.