I had nagios configured to know that this was a holiday:
monday -1 may 00:00-24:00 ; Memorial Day (Last Monday in May)
As far as I can tell it didn't work on Monday because I received some alarms, no big deal, I can ignore those. But now I noticed that those alerts were not running today (June 1). I removed the line and now they're running again. This is straight out of the example timeperiods.cfg, but maybe the docs are incorrect.
Does anyone have a timeperiod config for Nagios that works for holidays like "last Monday in may" or "fourth Thursday in November"?