Even if you diligently followed all the instructions in this book, you might encounter problems while upgrading. I can’t anticipate every difficulty you may have (or provide solutions in every case), but here are some of the most likely issues and how to deal with them.
If the Mojave installer icon has a slash through it, or if you try to run it and it quits immediately, the likely causes are:
You’re trying to run it on a Mac whose CPU is incompatible with Mojave (see Model Support for full details). Solution: Buy a new Mac. (Sorry.)
The installer didn’t fully download, or the file was damaged. Solution: First delete the installer. Then open the App Store app, click Purchased, and ...