KW> I'm wondering if there's a way to have either the Proxmox system or the
KW> Synology system connected to the UPS and shut down the other one?

I think APC makes software that does that, but likely wants to charge for it.
One UPS power failure can trigger an event to do multiple things.  

I never got that fancy with my setup and I have (10) APC UPS units over here. If
my power it out long enough for them to go out, everything just powers off
immediately.  I would try and do a clean shutdown, but even if it goes down hard
I have not had issues with my ESXi server/VMs.  Worst case, I could restore
things.

- Mark

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