Turn Off Anti-Malware Software

In general, anti-malware software doesn’t interfere with purchases and upgrades from the App Store. However, when Apple released Mountain Lion, users reported that the Ad Banner Filter in Intego’s VirusBarrier software sometimes interfered with the process of downloading the installer. Something similar could happen again, and other anti-malware apps could also conceivably prevent Mojave from downloading properly. So, the easiest course of action is to turn off any anti-malware software you may have until you have downloaded Mojave successfully, and then turn it back on.

Obtain the Installer

Depending on your situation, obtaining the Mojave installer may be a trivial matter of a few clicks, or it may be an involved ordeal.

Copy the Installer to a Safe Place

Unlike most software that you download from the App Store, what shows up in the /Applications folder after you download Mojave is an installer (an app called Install macOS Mojave); you must run the installer to put all the necessary pieces in place. During this process, something surprising happens: the installer is deleted! That’s right—once Mojave is up and running, if you look in /Applications, the installer will be gone.

I presume the reason for this is that once Mojave is installed, Apple wants to give you back the 5.7 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 Mojave 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!

Now, before going any further, I should add some nuance to the “Mojave installer deletes itself” concept. The installer deletes itself only when both of the following are true:

• The installer is in /Applications on your startup volume.

• You do an in-place upgrade of your startup volume.

If you put the installer anywhere else—your desktop, ~/Downloads, or wherever—it won’t be deleted after it runs. Even so, because that big file is valuable, I urge you to make a copy just in case the unexpected should happen.

So, before you do anything else, you should either ⌘-drag the installer to move it from /Applications to another location (so it won’t be deleted automatically, no matter what), 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.

Make a Bootable Mojave Installer Volume

This step is entirely optional, but some people find it useful.

The Mojave installer doesn’t include or require boot media. But you might want to have a copy of the installer on a bootable disk as a backup, to simplify installing Mojave on multiple Macs, to install Mojave on a Mac without Snow Leopard or later, or for other reasons.

The easy way to create this sort of disk is to use an app that does all the work with a few clicks—all you’ll need is a blank USB thumb drive, SD card, external hard drive, or other storage device with a capacity of at least 8 GB. Two apps that can do this, both free, are Install Disk Creator and DiskMaker X.

The other option is a command-line tool called createinstallmedia that is buried inside the Mojave installer (and thus is a method that Apple officially sanctions). Using this tool requires mucking around in Terminal—and it won’t work in Snow Leopard—but it requires no help from third-party apps.

Roman Loyola explains how to use both approaches in his Macworld article How to create a bootable macOS Mojave installer drive.

But there’s a catch, in that a bootable installer requires a full Mojave installer to work with, and in some cases, that’s not what you get when you download Mojave, as I explain in the sidebar ahead.

Update Your Duplicate (Again)

Earlier in this book, I instructed you to make a bootable duplicate of your startup disk and then—after performing some cleanup tasks—to update that duplicate so it reflects the current state of your disk. If you did that just minutes ago—and your bootable duplicate includes the Mojave installer file located outside of the /Applications folder—then you can move along to the next step. Otherwise, I suggest updating your duplicate one last time before running the installer.

Turn Off (Yes, Off) Automatic Duplicates

Picture this: shortly after you upgrade to Mojave, your backup software (which is still installed, natch) runs at its scheduled time, overwriting your bootable duplicate with a copy of your Mojave installation. And then, an hour or two later, you discover that Mojave has a major problem that requires you to go back to your previous version of macOS. But oops! The backup of your older system is already gone.

So, although you should certainly continue updating your duplicate after Mojave is installed, either do so using a new backup drive or wait a few days or so to make sure everything is working well enough under Mojave that you are unlikely to go back to your old system. Then, and only then, turn automatic duplicates back on.

Make a Copy of This Book

You’ll want to refer to this book while you perform your installation, especially if something goes wrong during the process. If you are reading on the Mac where you’ll be installing Mojave, if possible, you should either copy it to another computer, iPhone, iPad, or other mobile ebook-reading device, or print portions of it.

For tips on copying this book to a mobile device, read Device Advice (popular methods include Dropbox and downloading directly to the mobile device from your Take Control account). To download this book in a different format, click the link in Ebook Extras.

If you print to paper, you can limit the printout to just these chapters (as appropriate to your situation): “Upgrade Using Plan A: In-place Upgrade,” “Upgrade Using Plan B: Clean Install,” “Perform Post-installation Tasks,” and “Troubleshoot Upgrade Problems.”