Apple’s Time Machine is a neat little utility to automate onsite backups. However its machinations are, like so many of Apple’s products, completely opaque to the end user using the standard user interface and so troubleshooting can be rather difficult. Fortunately for us, this is one of those circumstances where Terminal commands can come to the rescue.
Our first magic spell is…
log show --predicate 'subsystem == "com.apple.TimeMachine"' --info
This will show logged message from the past and can be useful if you’re trying to troubleshoot an issue that’s already in progress. Run this command and macOS will display the last few weeks of Time Machine logs before exiting
The second magic spell is…
log stream --style syslog --predicate 'senderImagePath contains[cd] "TimeMachine"' --info
This command will run – and will remain running until you explicitly exit it – and will display any log messages that Time Machine writes out to the system log.