Tech 101: Everything you need to know to verify Time Machine backups (2023)

You're trying to use Time Machine to keep up-to-date backups of your Mac data, but there's a nagging concern in the back of your mind. How do you know that the backups are good?

That's a good question we should all ask about our backups. There are several ways to make sureTime Machine backups are in good condition, and we will cover most of them in this guide.

Before we move on to verifying the integrity of your backups, there is an important distinction in Time Machine technology that you should be aware of. a line in the sand, if you will. Time Machine backups created on OS X Yosemite and earlier have more limited backup testing capabilities than those created on OS X El Capitan and later. We have included notes on which version of the Mac operating system the verification method works on. Let's start with that.

Check Time Machine hard drive
Before we try to verify the files in a Time Machine backup, you need to make sure that the Time Machine hard drive has no problems. Begin withturn off the time machineand then use Disk Utility First Aid to check if your Time MachineThe disc is in good condition.🇧🇷 If errors are found, use the "Repair Disk" option in Disk Utility as described in the link above. (Need dedicated Time Machine storage?these external solutionsto find the perfect drive for your Mac).

The eyeball method of checking the time machine
This somewhat simplified way of checking the status of your backups is done by using Time Machine to restore one or two files and then checking (looking at) the files to see if they appear to be intact. Before you complain that this method doesn't sound very reliable, you're absolutely right, but it does provide a quick and easy way to verify that the basics of Time Machine and your backups actually work.

The eyeball method works for any version of Time Machine or Mac OS. The only requirement is that you have a Time Machine backup on your Mac:

Access Time Machine by choosing "Enter Time Machine" from the Time Machine menu or by launching the Time Machine application located in the /Applications folder.

Use the arrow in the Time Machine window to go back to an earlier time.

In the Time Machine Finder window, right-click a file and select Restore "File Name" to... from the pop-up menu.

The time machine shuts down.

After a moment, you'll be presented with a standard Finder picker, where you can choose a location to save your Time Machine file. Navigate to the location where you want to save the file and click New Folder. We strongly recommend creating a new recovery folder, as there is a bug in some versions of Time Machine that causes all files that occupy the same folder as the selected file to also be recovered. Restoring to a new folder isolates the file when the error occurs.

The file is restored to the new folder location.

Open the recovered file and examine it to make sure it is in the correct format. This can be as simple as viewing the contents of a document, previewing a recovered image, or checking the file size and creation date.

If the file or files look fine and no disk errors are detected when you run Disk First Aid, you can be sure that your Time Machine backups are healthy.

To use:If you've run into any errors while using Disk First Aid, it might be time to investigate.spare discs🇧🇷 Unlike other storage media we use, we recommend not tolerating drive failures when backing up.

Check backups on Time Machine drives
Backup verification has been a built-in feature in Time Machine since 2009, when the first Time Capsule was released. Make sure your backups work for all versions of Time Machine and Mac OS since Snow Leopard.

But before you say "Yippie! Easy way to verify my backups!", the Verify Backups feature only works for Time Capsules, NAS (Network Attached Storage) that supports Time Machine, or attached external hard drives to a Mac on your network It can be deployed on the local network and running on your own Mac. If the Time Machine backup location meets any of the above criteria, you can run the verification function as follows:

Make sure Time Machine is available as a menu bar item. If not, open the Time Machine preferences window and select Show Time Machine on the menu bar.

Hold down the Option key and click the Time Machine menu bar item.

You should see the Verify backups option. If the option is grayed out, the Time Machine hard drive does not meet the requirement of being a Time Capsule, NAS, or remotely mounted external hard drive.

Select the Verify backups item.

Time Machine starts the verification function. You can observe the status of the verification process by opening the Time Machine settings window; a status bar shows the progress. If an error is discovered, Time Machine will notify you; Otherwise, no information will be provided, following the old adage that no news is good news.

Compare backups as tmutil
The following method to verify a Time Machine backup can be used instead of the backup verification method we just saw. It works for any type of Time Machine backup, not just Time Capsule or NAS, and it works for any version of Time Machine or Mac OS.

Unlike verifying backups, the diff function is performed byTerminal, with the tmutil command. It provides a file-by-file comparison of the last backup to your Time Machine disk with the current state of your Mac. As such, it would be very rare for the diff function to produce a 100% match, since there are almost always files on your Mac that update in the background.

Launch Terminal in /Applications/Utilities.

At the terminal prompt, type:

sudo tmutil compare -s

The -s option forces tmutil to only compare file sizes. You can have the diff function check for many additional file parameters, but since the diff is done on a file-by-file basis, it can take a long time; The file size limit helps save time and still get reasonable results. Still, the compare command can take anywhere from 20 minutes to a few hours, depending on the size of your backups.

🇧🇷 (file size) / path to file: The exclamation point (!) indicates a difference in file size between the backup and the archive on your Mac.

+ (file size) /path to file: The plus sign (+) indicates a new file that does not exist in the backup.

– (file size) /path to file: Specifies a file that was removed from your Mac but still exists in your backup.

The problem with the compare command is that it is time sensitive. As the time between the backup point and the current point increases, more and more files will be different. So while Compare can serve as a pointer when used directly after a backup, it quickly becomes less useful over time.

Verify checksums (OS X El Capitan and later)
Starting with OS X El Capitan, Apple added a method to verify files in the Time Machine backup, by comparing the checksums created by Time Machine when the files were backed up with a checksum derived from the actual files in the Time Machine backup. backup.

This is a file-by-file comparison, so the process may take a while. The tmutil function only generates errors and warnings when a problem occurs. If the backups match the stored checksums, the command simply exits with no results.

The command has the form:

sudo tmutil verifychecksums /path to the backup drive. For example, if I want to check my Time Machine drive, which is called Tardis, the command is:

sudo tmutilcheckchecksums/Volumes/Tardis

If you're not sure of the path to the backup drive, enter the first part of the command (sudo tmutil verifychecksums) and drag the drive from Time Machine into the Terminal app. The actual path to the drive is entered automatically.

To use: If you use the drag technique to enter the path, it will probably add an extra space at the end of the path. Be sure to remove the extra space before running the command. Otherwise, you may receive error messages about route enumeration errors.

Start Terminal, if it's not already open, and type the following at the Terminal prompt:

sudo tmutil verifychecksums /path to the backup drive

Be sure to replace /path to the backup drive with the actual path to the Time Machine backup.

Run the command by pressing Enter or Enter.

To use:If the Time Machine backup you are verifying was originally created with OS X Yosemite or earlier, the verify checksums option in tmutil will not work, even if you are verifying in a newer version of Mac OS, and will simply return an error.

The checksum option in tmutil returns it to the terminal prompt if there are no errors and essentially provides no confirmation text of any kind. On the other hand, if there are problems, Terminal prints messages indicating the type of errors found.

When should Time Machine backups be verified?
You probably don't need to check your backups every time Time Machine runs. However, it might be a good idea to review Time Machine when you first set up your backup system, change backup drives, or make other changes to your Mac or backup system. Of course, if you've never reviewed your backups before, now is a good time to give it a try.

Related article:Yes, you can use one drive for Time Machine and file storage

Tom has been an avid Mac user since Mac Plus. He is also known to dabble in the dark side, aka Windows, and has a well-deserved reputation for being able to explain just about anything to anyone. Tom's experience includes more than 30 years as an engineer, programmer, network administrator, software tester, software reviewer, database designer, and designer of computer networks and systems. His online experience includes working as a system operator, forum leader, author, and software library manager.