Many years ago, while I was working at Sun Microsystems, Inc. on adding POSIX-conformance into SunOS 4.1, I was making changes to the OS and utilities during the day and running complete builds of the system overnight (starting a build just before I left work in the evening). This worked fine for several weeks until one Monday night when the system died at about 8:30pm killing the build-in-progress. There was no core dump, no indication of any hardware problems, and restarting the build when I got to work Tuesday morning completed normally (taking a little over three hours to complete).
The same thing happened the next three days in a row, with the system always dying sometime between 8:20pm and 8:40pm.
I decided to stay at work late Friday evening to see if I could figure out what was causing the crashes. I went to the bathroom at about 7pm so I would be sure that I could be at my computer by 7:15pm and would be able to stay there until I found out why my computer was dying every night. When I got back to my office five minutes later, I found that my computer had been unplugged by a member of the cleaning crew so he could plug in the vacuum cleaner they used to clean the hallway and offices where my office was located. (The way my office was arranged left a power strip close to the hallway while other offices in my area had their power strips in less accessible locations.) I unplugged the sweeper, plugged my computer back in, and waited for the cleaning guy to come back to my office.
I found out that:
- the cleaning crew comes in an hour and a half earlier on Friday that they did Monday through Thursday,
- they got a new vacuum cleaner on Monday with a cord that wouldn't reach from the plugs in the conference room to the other end of the building, and
- unplugging a computer is inconsequential to a janitor if doing so allows him to sweep the carpets at the end of the hallway.