Replying to a message of Geo to Don Hills:

 >> As for having a "maintenance mode", you can IML it with
diagnostics if
 >> you have it to yourself but normal diagnostic and repair work is done
 >> with the processor running - you take the section of the complex that
 >> you need to work on offline via the service console and the machine
 >> just runs a bit slower until you put it back online. It's very
 >> uncommon to have to take
 G> the
 >> whole machine down for maintenance. It's part of the
"z" in zSeries.

 G> The way I discovered how to hack all the NEC mini systems was when
 G> reading the install manuals. Usually nobody is thinking security when
 G> creating sysgen utilities. Now I don't know squat about mainframes but
 G> if those utilities are still present after the system is up and
 G> running, it's completely possible they could be used as an entry
 G> point. Mainframes probably also have some remote maintenance interface
 G> that might provide a similar point of entry.

When I was an operator I had a system crash, the service processor phoned IBM
and the IBM support center called me before I had a chance to call them.  The
only remote maintenance IBM could do was to dial in through the service processor
and from there they could examine the system - the guy on the phone with me was
doing it and started telling me exactly which part had failed etc. etc. - I asked him
if he could dump all that to the technician who was enroute (so I didn't
have to write
it down) and he said sure, and did (it was a thermal sensor about the size of my
thumbnail).  This was 10 or 11 years ago IIRC, I don't know how they are doing it
now.

--- FleetStreet 1.19+