[9fans] serial reboot boxes

[erik quanstrom <quanstro@quanstro.net>]

i believe that apc power supplies have a serial connection and
should be able to cycle the power. it's been a while on those.

when i worked at ibm we had a watchdog program monitored
the serial line and rebooted the computer if CTS was high.
this might work for you if the kernel is still living, but some
of the services are confused.

- erik

Russ Cox <rsc@swtch.com> writes

| 
| (This is slightly off-topic, but since Plan 9 users seem to be the
| only ones using serial consoles anymore...)
| 
| At Bell Labs we have a handful of custom-built boxes
| that help reboot machines.  I never knew how they worked
| inside or even what the inputs and outputs were, but
| if you asserted CTS on a serial line connected to one,
| they'd make the attached computer reboot.  I think they
| were doing AC power cycling.
| 
| I built a box of similar functionality myself ten years ago.
| I went through a few designs but eventually ended up with
| a solid-state AC relay being driven by a serial line.  I saved
| a sketch of the circuit but have since misplaced it.
| I don't know where the box ended up either.
| I don't remember it costing very much money (certainly
| no more than $20) to buy the parts from Radio Shack.
| 
| I would like a few more of these.  Rather than build them,
| I went online looking for such.  I can't find any.  I found ones
| with ethernet controllers and web servers, but those are
| $300 apiece (usually for a handful of outlets), and all I
| really want is just one outlet and one serial port.
| 
| Does anyone know where to buy the simple version for cheap?
| 
| Failing that, does anyone know where to buy cheap solid-state
| AC relays?  The ones I've found have all been $100+, which
| doesn't seem right to me.
| 
| Thanks.
| Russ