Ever curious to see what files Time Machine is backing up right now?
Open up the terminal, and type this command (you’ll need your password):
sudo opensnoop -n backupd | grep -v 'Time Machine Backups'
Opensnoop watches the files that Time Machine accesses and tattles on it. I’m always surprised to see the files I’ve recently changed. Often times, I’ll be editing photos and generating gigs of new backups just by changing header information and it’s nice to know what’s going on there.
Hat tip to Bill Lipa.
Update Feb 2017: opensnoop doesn’t work on Mac El Capitan and newer. You can try this instead which appears to work:
sudo fs_usage -w -f pathname | grep backupd | grep "(R___"