Whether you’re considering using the macOS utility called Time Machine to back up your Mac or you’re already using it, you might be wondering what exactly it backs up.
After all, it would be tragic for your Mac’s hard drive to crash, only to find out what you thought you had backed up really was not backed up at all.
So what, exactly, does Time Machine back up?
Time Machine backs up your entire hard drive unless you specify otherwise.
Because of this, it’s easier to list what the software doesn’t back up. The utility excludes a few items from your backup, as we’ll detail below, but most of us will never need these files.
I often used Time Machine in my role as a Mac administrator, so I’ll provide you with all the specifics you need to know about Apple’s backup utility.
In this article, I’ll detail the specific files and directories macOS skips when backing up your hard drive.
Let’s get started.
Does Time Machine Back Up Everything?
For practical purposes, Time Machine backs up everything on your hard drive you would need. Nevertheless, the utility does exclude some files and folders.
Following is a list of what Time Machine skips when backing up your hard drive.
1. Non-Specific macOS Files
According to Apple, “Time Machine doesn’t back up system files or apps installed during macOS installation.”
Therefore any built-in applications like Maps or News aren’t backed up. This works in your favor by saving time and space on the backup device since these files can be re-downloaded from Apple if you ever need to restore your Mac.
Time Machine excludes generic operating system files that can be retrieved from Apple’s servers.
2. What You Tell Time Machine to Exclude
Once you have Time Machine set up and enabled on your Mac, you can specify certain folders you don’t want the utility to back up.
To exclude your downloads folder, for example, open the Time Machine pane in System Preferences and click on Options…
From the options window, click the + button, browse to your downloads folder and click Exclude.
Now click Save.
Any directories in this exclude list will not be backed up.
3. Photo Library Database
If you use the Photos app on macOS, the operating system creates a database folder inside your photo library. Time Machine does not back up this folder.
This does affect your photos or albums; Time Machine does back those up, and the database folder and contents can be recreated if you ever need to restore your Photos library.
4. Non-Local iCloud Drive Files
Time Machine only backs up what’s stored on your hard drive, so it follows then that any iCloud Drive files not locally synced won’t be backed up.
Never to worry, though. You can always retrieve a copy of the file from iCloud.
If you’re paranoid about data loss (not a bad thing!), I recommend downloading local copies of any critical files in your iCloud Drive. Then, the next time Time Machine runs its backup, those files will be copied to your Time Machine storage device.
5. Log Files
macOS stores system log files in the /private/var directory, which, by default, is excluded from backups. In addition, application logs and other report logs stored in /Library/Logs are not backed up either.
Generally speaking, you wouldn’t need these log files. But if you want a copy of them, manually copy them to a folder somewhere else on your hard drive, and then Time Machine will back them up.
Of course, you will have to remember to do this regularly, so it’s probably not worth the effort.
6. Cache Files
macOS caches various files to help speed up processes like loading webpages and applications.
Another name for these files is temporary files, and although they might optimize your computer experience, they are redundant and not necessary. These files are simple local copies of frequently accessed files. The OS can recreate them at any time.
Therefore, to save space on your backup drive, Time Machine ignores these files. The majority of temporary files reside in ~/Library/Caches. (The tilde references the current user account’s home folder.)
7. The Contents of Your macOS Trash
Time Machine ignores any files or folders in the Trash.
Again this is a space-saving technique. Apple assumes that if you moved the file to Trash, you no longer need it.
I recommend not placing any files or folders you might need later in Trash. You might laugh, but I’ve seen more than one person use the trash can as a storage repository. Don’t do it.
8. Spotlight Indices
Spotlight is the underlying search mechanism for macOS that allows you to search your hard drive for files or applications.
To search folders more quickly, Spotlight creates index files that help the OS know where your data is.
Just like with cache files, these are unnecessary, and Spotlight can easily recreate them.
Look in The Exclusions File
Every Time Machine volume keeps a hidden file called .exclusions.plist in the root of the backup folder. If you want to see exactly what’s excluded, open up that file in your favorite text editor program and view its contents.
Still have questions? Here are some you might be asking.
How does Time Machine work?
After configuring Time Machine for the first time by specifying and formatting a backup drive, Time Machine runs a complete backup of your hard drive–except for the exclusions we mentioned in this article, of course.
After that, the software will run incremental backups–backing up only those files that have changed since the last backup. The utility runs every hour and saves hourly backups for “the past 24 hours, daily backups for the past month, and weekly backups for all previous months.”
Time Machine will delete the oldest backups as the backup disk becomes full.
The great thing about Time Machine is once you get it set up, the utility runs automatically without any user interaction. It only bugs you when it hasn’t been able to access your specified backup device in a few days.
Does Time Machine back up disk images?
Yes, Time Machine will back up disk images (files with the .dmg extension) as long as they are not stored in a directory in the exclusions list.
Time Machine won’t incrementally back up files within disk images, so if one file changes inside your .dmg, the utility will detect a change and re-backup the entire disk image.
If your disk images are large, this can take up quite a bit of space, so be aware of this phenomenon.
Can Time Machine back up to iCloud?
Unfortunately no. Unlike the iPhone and iPad, you can’t back up your Mac to iCloud Drive. You can, however, sync important documents with iCloud. And as long as they’re cached on your hard drive, Time Machine will also back up those documents.
Conclusion: Time Machine Backs Up Everything You Need
Time Machine doesn’t back up everything, but you’ll probably never have a need for any of these excluded files and folders, even if your hard drive craters.
One piece of advice, though. Periodically, I like to verify my data is backed up properly by manually restoring a random file from Time Machine. Call me paranoid, but testing my backups gives me peace of mind that my data is recoverable.
Have you ever restored files from a Time Machine backup? What was the experience like?About Andrew Gilmore