The big red button
Back when I was a PFY a company I was working for had a server room with about 50 physical servers powered by a large UPS. One day, the UPS was having its' annual maintenance. Myself and the resident BOFH were escorting the UPS tech. The BOFH encouraged me to press the big red button labelled "EMERGENCY POWER KILL SWITCH". The BOFH assured me that it would do nothing as the UPS was in bypass mode.
So I lifted the guard and pressed the button. Not only did the server room go offline, the entire building (about 350 staff worked there) was shut down. We quickly hid, only to reappear when the rest of the IT team arrived to investigate.
We were offline for about two hours as the 'Elf'n'Safety people would not allow us to reset the old fashioned breaker in the basement until an electrician had checked the system. Luckily we had a few sparkies on staff so it didn't take too long.
They never discovered my dark secret.
Anon because.....
