The purpose of this guide is to help diagnose issues that arise when a Timemachine backup fails. This guide was written to help uncover why a given backup will fail, as the Timemachine interface simply reports «success» or «fail» at the end of the backup.
Each backup will go through the following process:
When watching the Timemachine backup happen via the console (see «Using the Console») each of the numbered events in the above image corresponds to the following console event (note: many of these are specific paths, identifiers to this example backup):
Knowing at which point in this process the failure has occurred will help to distinguish why the problem is occurring.
Start by opening the Console (console.app), which is found in «Applications» > «Utilities»
Next, you’ll want to filter the system log by a certain process: Time Machine. This is com.apple.backupd. Type the process name into the search bar at the top-right of the window. Now only events related to Time Machine will be displayed.
Start the backup
You should now see messages relating to the Time Machine backup in the console.
Note: This list will be updated as more errors are resolved
If you see this message:
X required (including padding), Y available
And the amount required is MORE than the amount available, then the backup will fail due to a lack of space for the backup data. In order to fix this, you will need to exclude files from the backup.