Erasing your Mac and installing a fresh version og OS X can be a nail biting experience. Especially since Apple suggests a completely different method than almost every other website and things can seem to go awfully wrong when following Apple´s advice. But relax and read this.
Disclaimer: This worked for me with Mac OS Sierra on a MacBook Pro Late 2013 , but it is not guaranteed to work on any hardware so check your Mac for compatibility with the latest Mac OS.
Macworld, Macrumors, Lifewire etc. all tell you to make a bootable USB and download and install the latest Mac OS from that if you want to format your hard drive. But Apple says you can clean install directly by holding Command+R (or Command+Option+R) on startup and then erase your startup disk without any external media.
The USB method is the old way of installing new operating systems and seems to be the most logic one, since erasing the drive should mean you cannot use the computer or internet connection. But it is actually not so. Apple cleverly made it possible to use Disk Utility to manage the the drive(s) and your wifi to access downloadable versions of MacOS even with your drive erased.
But many people who have tried to clean install with this method, are complaining that the installation process freezes on 6, 5 or 4 minutes. When that happens, you wished you had followed the other sites recommendations to download the OS onto a USB before you wiped the drive. Because you erased your harddrive, you cannot use Apple Store anymore to download anything. And it DOES seem that Apples way causes freezed installation. The problem may be real for some, but for me at least, it was just the a glitch in the installation graphics bar and a huge miscalculation from Apple on how much time was left of the installation.
After backing up your data, you follow apples step by step guide. To make sure my OS actually supported the Command+R function ( I have not upgraded the OS for a couple of years) I actually did a update installation of the latest os on App Store. This is maybe a waste of time, but it worked fine.
Check all messages in installer log
Then deleting the drive and doing a clean install, the download of the newest Mac OS starts all over. Only this time, it is extremely slow. So slow that the whole thing seems to stop. The time says 6 minutes, but the process can take hours and the process bar seems to be stuck. If you go to installer log, you see a lot of alerts that does not seem to be a good sign. However if you choose “All messages” in stead of only alerts, you hopefully see that the packages are being downloaded although the progress seemed to have halted.
For some people there seems to be a router/internet problem, that only a bootable USB would solve. If it applies to you, you could ask someone you know with a Mac or a Genius Bar to help you. For most people experiencing this, take a breath, then some more while you wait the necessary hours to go by.