Quickfix: Boot up screen stuck with spin freezes after Mac OS Sierra upgrade

After a major upgrade of Mac OS Sierra, my MacBook didn't boot up anymore. It freezes on the grey screen with dead spinning wheel.

After checking any non-apple Kext module in Safe mode and fixing any disk error in DiskUtility in Recovery mode, I nearly have no clue on what's happening to the hard drive.

Here come across 7 steps which can be useful for anyone who cannot resolve the boot up problem after upgrading to Sierra.

1. Shut down your Mac.
2. Press the power button to start up your Mac.
3. Immediately Hold down Command-S for single-user mode.
4. On the terminal window Type fsck –fy and press return
5. Type mount –uw and press return
6. Type touch /private/var/db/.AppleSetupDone and press return
7. Type exit and press return

Through Steps 1 to 3, you should have launched your Mac on a Single user mode.

In Step 3, the screen shows up the raw booting messages which show clearly what is running behind the scene.

Steps 4 to 7 will help check for file system consistency and remount the boot volume.

Regarding Step 6, what's point of creating empty file .AppleSetupDone?
Every time OS X boots, it checks for the existence of a file known as .AppleSetupDone. This empty file is created after the completion of Setup Assistant. It doesn't exist on a brand-new, out-of-the-box Mac, nor on one that has had a clean installation of OS X.
By removing this file, OS X will assume that Setup Assistant has never been run and will launch it as soon as OS X boots.
Setup Assistant is also run with root privileges, which is why it can create a new user account with administrator privileges without the need for any authorisation.

As I have gone through the wizards of Setup Assistant before bootup problem is encountered. I have not seen any wizard of Setup Assistant again.

After step 7, my MacBook booted into the logon screen which I usually see. I quickly login, and then restart it to see if things are working again. Finally, it booted up quickly and successfully to logon screen and let me login as usual.

As of writing, I can boot back into my Mac OS Sierra v10.12.2.