I have a late 2011 iMac 2.5GHz Intel Core i5 with 12 GB RAM running OSX 10.8.2. When I type in the command last in OSX's Terminal I get a long list of logins, reboots and shutdowns. However, very many of them - more than half - have the status crash instead of the logout/shutdown time. Thing is, my Mac hasn't crashed even once. My last shutdown earlier today has also been logged as a crash. What gives? Can it safely be ignored? In the Console->system.log I get the Previous Shutdown Cause alternating between either 0 and 5 (most of them are 0). What do they stand for? I should mention that I recently got my iMac's logic board replaced (old one just died on me, was covered by Apple care). However I did reformat and reinstall everything after that, so I doubt the logic board is a factor. Also, I do disconnect the iMac from the mains when it's not in use (as in, I switch off the UPS) due to frequent power cuts (I don't want the UPS beeping in the middle of the night). Could that be causing the PRAM / NVRAM / SMC or whatever to play up and thereby be causing all this? Though it has logged restarts as a crash many times too. Any ideas about what is going on?