[HECnet] How long has your 20 been up?

[Paul Koning]

> On Jan 18, 2022, at 2:05 PM, Thomas DeBellis <tommytimesharing at gmail.com> wrote:
> 
> ...
> I wrote TIMET2 because I needed to know when to set a shutdown.  If you don't do that and you hit the uptime limit, then the machine simple crashes with an UP2LNG BUGHLT.

Oops.

> I know that XKL fixed at least part of the uptime problem, but I don't remember what that limit is.  What are the limits for other systems?

It's not overly strange that designers of mainframe systems, where planned shutdowns (say, for preventive maintenance) were a regular occurrence) would overlook silly bugs like that.  It feels like the sort of thing that minicomputer software, especially real time systems, would never do.  For example, RSTS has no uptime limit.

Another mainframe system that had weird behavior, though not an actual hard limit like this, is the CDC 6000 mainframe NOS system.  The one I worked on (University of Illinois PLATO) was shut down for PM every weekday morning, so normal uptime was less than a day.  But the Cyber1 system, running that OS in emulation, was up for months on end until we instituted weekly backups.  That exposed a leap year bug: if the system was started in January of a leap year, it would mishandle February as 28 days rather than 29.  It would do it right if started in February, or before January.  I wrote a patch for it, just for completeness.

	paul