I manually put my iMac to sleep before going to sleep myself last night. It's set to do so automatically, but I kept it awake for quite a while, as I was busy doing work. It's also set to wake up at about 8:30 in the morning. Today I discovered that the iMac was off...somehow, it shut down. There was no overnight power outage (clocks still working, no power-failure indications on other appliances). I restarted via the power switch (at 10:12 AM). After the machine booted, it created a log entry regarding the shutdown: Feb 18 10:12:11 localhost kernel: Previous Shutdown Cause: 3 FWIW, later, when my next scheduled TM backup kicked in, it took quite a while for it to complete its backup. Apparently, there was a need to do a "deep traversal": Feb 18 12:05:06 nicks-imac /System/Library/CoreServices/backupd: Node requires deep traversal:/ reason:kFSEDBEventFlagMustScanSubDirs|kFSEDBEventFlagReasonEventDBUntrustabl e| Any idea what this means?