We’re going to talk about installing a version of your Mac’s operating system (OS), known as “macOS” or “OS X,” on your Mac, older than the one you’re currently running, on a partition of your primary hard drive or on an external hard drive. You may find that your current instance of OS X is too unstable for normal day-to-day usage or more heavy-duty tasks like development. Remember all the problems people had when they upgraded to OS X 10.13, also known as “High Sierra?” Oy, vey. You might have been like “Get me the heck outta Dodge!” You wanted or needed to get back to a stable OS, like Sierra (OS X 10.12) or El Capitan (OS X 10.11). For developers, you may have to install an older version of Xcode not supported by your latest OS. For Cocoa/macOS developers, you may need to make absolutely sure that your desktop apps are backward compatible, and the only way to do that for sure is to install and run your apps on older versions of macOS. I will show you, step by step, how to get a valid copy of an older version of macOS, make a bootable installer disk, and install the old OS.
Note to iOS developers
As iOS developers, you’re probably mostly concentrated on using Xcode and perhaps a few supplementary Mac apps, like Safari, TextEdit, or Pages, to develop apps for iPhone (iOS), iPad (iOS), Apple Watch (watchOS), and Apple TV (tvOS). You probably heavily use Git, Xcode command-line tools, or development tools like CocoaPods. If you’ve been developing for more than even a year, then you know that Apple pushes out a new OS about once a year and also pushes out a new Xcode version once a year. It behooves you to know something about OS X. So while this tutorial is of course open to anyone who needs to roll back their OS, my core audience of iOS developers should give it a read and consider practicing developing some macOS apps. There are millions of people out there with Macs. That’s a big potential target audience for whom you can build apps.
Obeying the rules
I’m pretty sure that according to Apple’s rules, you can only run one version of OS X on one Mac at a time. Be sure to consult Apple’s End User License Agreement and its Terms and Conditions before proceeding. As we’ll see in a bit, they do allow you to download old versions of OS X that you previously purchased and/or downloaded through the Mac App Store using a valid Apple ID.
Finding an old version of OS X
Only you can decide which old version of OS X you want to install, but you can’t just grab any version from any time period and install it on any Mac.
You need to know if your Mac’s hardware is compatible with the old version of OS X you’ve chosen to install. Here’s a hardware compatibility list for OS X versions 10.6 (Snow Leopard), 10.7 (Lion), 10.8 (Mountain Lion), 10.9 (Mavericks), 10.10 (Yosemite), 10.11 (El Capitan), and 10.12 (Sierra). Here are the requirements for the latest OS X 10.13, High Sierra.
Finding and downloading an old macOS version
You can only get old versions of OS X that you previously downloaded/installed on one of your Macs using your valid Apple ID. Go to the App Store app on your Mac and then select the Purchased tab. Look for the version you want — and one that’s in the list (obviously). Using my Apple ID and browsing my Purchased history, I’m going to get OS X Yosemite by clicking the DOWNLOAD link as show here:
You’ll get a warning that “A newer version of OS X is already installed on this computer. Are you sure you want to download OS X 10.10?” Click Continue as shown:
This will start the download of Install OS X Yosemite.app into your /Applications folder. This file is 5.72 GB, so expect the download to take awhile.
Preparing to install the old macOS version
If you double-click on Install OS X Yosemite.app, you’ll get the warning, “This copy of the ‘Install OS X’ application is too old to be opened on this version of OS X.” Here’s what you’ll see:
Never fear. We can do this!
Creating “a bootable installer for macOS”
Apple has the answer to how we’ll make use of the installer (OS X Yosemite.app) we downloaded. They have a page entitled “How to create a bootable installer for macOS.”
What we’ll do is follow Apple’s advice and “use an external drive or secondary partition as a startup disk from which to install the Mac operating system.” The best way to create a “startup disk” is to use a USB thumbnail drive with “at least 12GB of available storage.” Everything on your USB drive will be erased, so back it up if you need the files contained on it.
In a nutshell, we’re going to use an Apple command, available only from Terminal, that will turn our USB stick into a bootable drive and copy that OS X installer we downloaded to the USB stick.
When I got that USB stick with at least 12 GB of available space, I inserted it into an available USB port on my Mac. The stick was mounted in my OS X 10.13 file system as “/Volumes/Untitled” and showed up in Finder as “Untitled” as you see here:
Now that I had that USB stick mounted, it was time to continue with Apple’s advice. I made the USB stick into a bootable drive containing all the OS X Yosemite installation files.
I was able to copy the command I needed to do this straight off Apple’s page. Here’s their version of the command:
$ sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
Notice that all I had to do was change the reference to “MyVolume” in Apple’s command to the name of my USB stick, “Untitled”:
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
All those forward slashes are just indicators for the command-line interpreter that a space is being used.
For example, Install OS X Yosemite.app in the /Applications folder becomes “/Applications/Install\ OS\ X\ Yosemite.app”. I’m not going into all the dreary details. If you’re interested in what the
createinstallmedia command does, read here.
I opened a Terminal window and pasted my
createinstallmedia command to the prompt and pressed the return key.
You’ll get — WOW — animated textual feedback while
createinstallmedia prepares your USB stick:
$ sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
Ready to start.
To continue we need to erase the disk at /Volumes/Untitled.
If you wish to continue type (Y) then press return: Y
Erasing Disk: 0%... 10%... 20%... 30%...100%...
Copying installer files to disk...
Making disk bootable...
Copying boot files...
This first time I ran this command, I got an error re: the USB drive can’t be erased. I knew that meant that I had the drive open in Finder and/or Terminal, so I closed everything that could’ve possibly been holding onto file handles on the USB drive.
Deciding where to install the old macOS
You can choose and configure the location (disk/partition) on which you want to install your old macOS version. This can be done from the installer on the USB drive. It has features like Disk Utility built in to it. But I like to plan ahead. I started Disk Utility before using the USB stick to create a new partition on an external USB SSD for my new Yosemite instance to live, as you can see here:
I went crazy creative and named my new partition… “Yosemite” 😉 . You can also create partitions on your internal drive for installing your older version of macOS. Just be sure you have enough room.
Installing the old macOS version
It’s time to install the old version of macOS.
- Make sure your bootable USB drive is inserted into an available USB slot and is mounted. If mounted, you’ll see it in Finder as I showed previously.
- Restart your Mac. When you hear the Apple “chime” sound, immediately hold down the option (⌥) key so that your Mac will bring up the Startup Manager. This feature shows you all your Mac’s bootable media. Remember all the business we went through to download Install OS X Yosemite.app and then used the
createinstallmediacommand? Choose the bootable disk labelled “Install OS X Yosemite” by clicking on that drive icon once (which selects it). Once selected, the bootable drive has an arrow pointing to it. Click the arrow to boot into Install OS X Yosemite as you can see immediately below:
- Your Mac will think for a little bit:
- Install OS X Yosemite.app will start up. Notice there are several choices you can make and several menus. These are various utilities you can use when troubleshooting an install:
- From the dialog box in the middle of the screen, choose Install OS X and the click Continue:
- And now, for something completely different… you’ll get the Yosemite installer’s splash screen. Click the Continue button:
- Agree to and then agree to the license:
- Choose the partition on which you want to install Yosemite. Remember I set up a partition on an external drive named “Yosemite.” Click the partition you want and then click Install:
- The installation process will start so be patient:
- NOTE: If you see the previous screen hang at “About a second remaining,” don’t panic. The installer probably didn’t estimate the length of time for the install perfectly. Be patient and wait. Only force a restart if you get into a situation in which you’re waiting for hours.
- Your Mac will automatically restart and keep thinking:
- This Yosemite installer progress screen will appear and chunk through more of your installation:
- Remember that I mentioned installer utilities above? If you run into problems, not only can you use those utilities, but you can look at the output from the installer itself. You may find messages in the logs that help you resolve an installation problem. You can look at the logs by going to the Window -> Log menu or by hitting the ⌘ + L key combination. You can save the log(s) to another partition for later inspection:
- Your Mac will automatically restart and keep thinking:
- Finally you’ll get the “Welcome” screen where you can finish — and configure — the installation:
The rest of the installation and configuration of your new instance of Yosemite is easy stuff:
– Select your geographical region
– Select your keyboard layout
– Set up your Wi-Fi connection
– Optionally transfer data from another partition to your new instance
– Sign in with your Apple ID
– Agree to agreeing to the license … again 😉
– Creating the first user account
– Decide whether you want to share diagnostic and usage data with Apple
- Once done with all the installation configuration hoo-hah, you’ll have a brand-spanking-new version of Yosemite to use. After my initial boot-up, I went to the Apple menu and selected About This Mac:
Notice the message in the upper-right corner of my screen reminding me that there are updates for my OS version. Remember we installed the base version of Yosemite (10.10), and these OS’s almost always have updates and patches (e.g., 10.10.5). I suggest you install all OS X updates recommended to you by the Mac App Store.
You’ve got a new operating system installed. Pretty cool. Remember the complexity of an install can depend on which version of OS X you installed. You may have issues with older ones. But, then again, look at High Sierra. Lots of people had problems with installing it. Leave a comment if you need help. I’ll do my best.