I sometimes get Time Machine errors that say something like “Backup failed” or “Unable to complete backup” or “An error occurred while copying files to the backup volume.” How am I supposed to interpret what these error messages mean?

In its desire to make Time Machine as simple as possible, Apple seems to have brought that simplicity to Time Machine’s cryptic error messages as well. This is somewhat unnerving, since an error with your backup system could mean the difference between you successfully restoring a file or not. Luckily, if you poke a little bit under the hood, you can find out more extensive details about what your Time Machine error messages are really trying to tell you.

Time Machine Buddy is a handy Dashboard widget for viewing your Time Machine system logs.

Launch Console (in /Applications/Utilities), click Show Log List, click All Messages at the top of that list, and then filter for backupd in the search field. You’ll then see all of the system logs generated by Time Machine, both successful and unsuccessful. You might need to do a bit of Internet research to figure out what the error numbers mean—for example, a Google search informed me that an error of -43 indicates that a file has been changed or deleted since the backup started.

TM Error Logger comes with a great reference guide for all of Time Machine's error numbers.

Looking to avoid that busywork? TM Error Logger (donations requested, www.carnationsoftware.com) will give you an easy-to-read error report for the current and previous Time Machine logs. It also comes with a complete reference guide to all the Time Machine error numbers. The Dashboard widget Time Machine Buddy (free, www.bluedog.com.au) goes even further by splitting up all of your Time Machine logs into readable reports. The widget shows you both errors and successful backups, and can even tell you how long each backup took.