An in-place upgrade to macOS 27 Golden Gate is safe enough. Most people will never think about it again. But a few things can cost you data if you meet them unprepared. An installer that deletes itself. A backup that cannot restore what you excluded. A recovery mode that will not take you back.
Here are the step-by-step instructions that you should follow to upgrade to macOS 27 without losing data. I tested these fifteen steps on my Mac rather than rehashing apple’s instructions. The first eleven happen before you click Install.
1. Check your apps first
RoaringApps maintains a wiki that lists thousands of Mac, iPhone, and iPad apps and the current status of their compatibility with various operating system versions (including macOS 27), as reported by users. Although this list is neither exhaustive nor definitive, it provides a quick way to check on the apps most important to you.
Remember to check for updates of setting panes, status menus, browser extensions, and other system enhancements too.
2. Update apps before, not after
The installer looks for, and disables, certain types of incompatible software—but there’s no guarantee it will find everything. Given the choice, you’re usually better off upgrading third-party software before you install a new version of your operating system. (You may occasionally run into an app with a newer version designed to run only on macOS 27; in such limited cases, you may have to install the updated software after upgrading to macOS 27.)
3. Clear Time Machine exclusions
The most important drawback for our current purposes is not a flaw in Time Machine as such, but rather the fact that, for any of numerous good reasons, you may opt to exclude some items from Time Machine (by going to System Settings > General > Time Machine > Options and adding files or folders to the Exclude from Backups list). If you do that, those files can’t be restored if and when you have to revert to an older version of macOS. So, fair warning: you can use Time Machine if you like, but first remove everything from that list and make sure Time Machine completes at least one run.
One type of backup that will not suffice for this particular purpose is an online backup using a service such as Backblaze. I like Backblaze and use it myself, but because it excludes many types of files and is unavailable to the macOS installer or Migration Assistant as a data source, it can’t be used to restore an entire Data volume after a failed upgrade.
4. Do not use Software Update
Apple offers major upgrades through Software Update, and a badge appears on the System Settings icon. You can use it, but I recommend against it:
- The downloads may be smaller, but you don’t get a standalone installer. That means you can’t copy it to another Mac or make a backup of the installer in case you need to use it again .
- As a consequence of not having a full installer app, you can’t make a bootable installer .
- The installer you get via Software Update does not prompt you to choose a destination ; it can be used only for updating the copy of macOS on your current startup volume. That also means this approach can’t be used with a clean install. So, if you try using Software Update for an in-place upgrade and you have a problem, you’ll have to download the full installer anyway to switch to Plan B.
5. Download from Apple only
The easiest way to proceed is to obtain a direct download link that points directly to Apple’s servers. I can’t overemphasize how important it is to download directly from Apple. Apple doesn’t publicize such links, but the site Mr. Macintosh has very helpfully collected them for us. The site Mr. Macintosh collects the correct links; they all point to swcdn.apple.com, a legitimate Apple download server.
6. The installer installer
You might be thinking, “Don’t I want an app called Install macOS 27? What’s InstallAssistant?” In fact, InstallAssistant.pkg is a simple installer that merely puts the Install macOS 27 app in your Applications folder. So, once that file has finished downloading, double-click it and follow the prompts to run the installer, which is really the installer installer. When it’s done, you’ll see Install macOS 27 in your /Applications folder, unless you chose a different location. You can then delete the InstallAssistant.pkg file.
7. Move the installer somewhere safe
I presume the reason for this is that, once macOS 27 is installed, Apple wants to give you back the 21 GB or so of disk space the installer was taking up, since you likely won’t need the installer in the future (and can download it again if you do). But what if you want to install macOS 27 on multiple Macs—or reinstall it later on the same Mac—without having to download that huge installer again? I’ll tell you what: you’d better put that installer in a safe place before you run it! If it’s anywhere else—your desktop, ~/Downloads, or wherever—it won’t be deleted after it runs.
So, before you do anything else, I suggest that you either ⌘-drag the installer to move it from /Applications to another location, or Option-drag the installer to copy it to another location—preferably another volume—so if it is deleted, you’ll have a spare. Or, create a bootable installation volume, as I describe next.
8. A bootable installer needs 32 GB
To move ahead with a bootable installer volume, you’ll want a flash drive with at least 32 GB of free capacity. (A 32 GB USB flash drive can be found for under $10 online or at your favorite local electronics store.) Then you follow a simple procedure to put a bootable installer on that drive and, when the time comes, start from that volume and run the installer.
Next, you’ll use a command-line tool called createinstallmedia that is buried inside the installer (and thus is a method that Apple officially sanctions). Using this tool requires a visit to Terminal, but it’s really a matter of copying and pasting one line from Apple’s website into Terminal and replacing the name MyVolume with the name of the drive you’ll be using. Apple offers complete instructions, and they’re not painful at all.
9. Two things before you start
Before you run the installer, if you haven’t already done so:
- If you are installing onto a laptop, connect its AC adapter to a power source. (If you forget to do this, the installer will prompt you.)
- Quit all open apps. (The installer attempts to do this for you—and prompts you if it can’t—but you might as well take care of this beforehand.)
10. Ignore the time estimate
If you insist on watching the installer’s progress bar gradually make its way across the screen, beware: its time estimates (“About 43 minutes,” “Less than a minute,” etc.) are notoriously inaccurate, especially near the beginning and end of the process. And remember: a watched installer never boils.
11. Where your old software went
The macOS 27 installer automatically checks for certain categories of incompatible software and moves any such files safely aside into a Relocated Items folder in /Users/Shared.
The installer can’t know about every potential software conflict with macOS 27—it disables only software that loads automatically on startup and that runs in the background, such as drivers and other kernel extensions. Ordinary apps are never moved aside, even if they can’t possibly run under macOS 27.
12. Confirm the upgrade finished
Not sure whether you’ve successfully upgraded since you missed the end of the process? Choose Apple menu > About This Mac. If the window says 27.0 or higher at the top under “macOS,” you’re running macOS 27!
13. Safe mode, step by step
If your Mac will not start, safe mode disables some third-party software and checks your disk for certain types of errors.
To enter safe mode, choose Apple menu > Shut Down and wait until the Mac has fully shut down. Then press and hold the power button until you see “Loading startup options” on the screen. When the Options icon appears, select your startup disk, hold down the Shift key, click Continue in Safe Mode, and then release the Shift key.
If macOS 27 starts up normally after a safe boot, a third-party extension or startup item may be the culprit. Check in /Library/LaunchAgents, /Library/LaunchDaemons and ~/Library/LaunchAgents for third-party items that haven’t been updated recently (older items are more likely to have compatibility problems).
14. Why recovery mode cannot downgrade
Even though you can do lots of things after starting in recovery mode—including reinstalling macOS—you probably can’t use recovery mode to downgrade to your old version because recovery mode doesn’t let you install arbitrary previous versions of macOS. Your only option is the most recent version of macOS that will run on your computer: probably not what you need.
In case you were thinking you can restore from a Time Machine backup in recovery mode and use that to get back to your older system…sorry, but no. Although Time Machine used to back up your full startup volume, ever since Big Sur, it backs up only your Data volume, not macOS itself. That’s why a Time Machine backup alone can’t restore an older version of macOS.
15. Build an older installer
If you have to downgrade to, say, Tahoe, and you don’t have a bootable duplicate or a bootable installer volume, you’re not necessarily out of luck. While running macOS 27, you can still download the Tahoe installer and use it to create a bootable Tahoe installer volume. The same goes for older versions of macOS.
For everything the release changed, see the complete guide to macOS 27 Golden Gate. There are also 35 changes that owe nothing to AI.
Now that you know how to upgrade to macOS 27 Golden Gate without losing data, there are 13 smaller tips worth knowing about the release. There is also a complete guide to macOS 27 Golden Gate that I recommend you check out.
