Before you install a major macOS update, take a proper backup. It is the least exciting part of updating your Mac, but it is the part that saves you if an install fails, an app behaves badly or a file goes missing afterwards.
For most people, Time Machine is the easiest option. It is built into every Mac and backs up your apps, photos, documents, accounts and settings to an external drive. Here is how to do it properly before updating macOS.
What you need before you start
You need an external drive that can connect to your Mac through USB-C, Thunderbolt or an adapter. Apple recommends a backup disk with at least twice the storage capacity of your Mac. So, if your Mac has 512GB of storage, a 1TB external drive is a sensible minimum.
If your drive contains important files already, do not select it blindly. Time Machine may need to erase and format a new drive before using it as a backup disk.
How to back up your Mac with Time Machine
- Connect your external drive directly to your Mac.
- Click the Apple menu in the top-left corner and open System Settings.
- Click General, then Time Machine.
- Choose Add Backup Disk.
- Select the external drive you want to use and follow the prompts.
- Choose encryption if you want the backup protected with a password.
- Wait for the first backup to complete before installing macOS.
The first Time Machine backup can take a while, especially if you have years of photos, downloaded files and large creative projects. You can keep using your Mac while it runs, but do not disconnect the drive.
How to check that the backup is complete
Open Time Machine in System Settings and look for the latest backup time. If it says the backup is in progress, let it finish. You can also look for the Time Machine icon in the menu bar, where macOS will show the most recent backup.
For a little extra reassurance, open a Finder folder with a file you care about, then enter Time Machine and make sure you can see an older version of that file. You probably will not need it, but it is better to find out now that the backup is working.
Should you use iCloud instead?
iCloud Drive is useful, but it is not a replacement for a full Time Machine backup. It keeps selected files in sync across devices. Time Machine is the better safety net before a macOS update because it can restore your apps, accounts, settings and files if something goes wrong.
My setup would be simple: keep iCloud Drive on for the files you need everywhere, then make a fresh Time Machine backup before every major macOS release.
Three things to do before installing macOS
- Keep the backup drive connected until Time Machine confirms the latest backup is complete.
- Make sure your Mac is plugged into power and has enough free storage for the update.
- Check that essential work apps, audio plugins and accessories support the new macOS version.
What if your Mac will not start after the update?
A Time Machine backup gives you options. You can restore individual files, migrate your data to another Mac or restore the Mac from Recovery if you need to start again. That is why I would not skip this step for a major update, even if your Mac has been reliable for years.
Back up your Mac before a macOS update: final word
Connect an external drive, run Time Machine and wait for it to finish. That is the whole job. It can take an hour or several hours depending on your files, but it is much easier than trying to recover something after an update has gone wrong.
- SourceApple: Back up your Mac
