Changed /etc/fstab, now stuck in login

Solution 1:

You can try booting to safe mode where you can make changes in a GUI environment, or booting to macOS Recovery where you can make changes from Terminal.

If you need to do it from macOS Recovery, once booted to macOS Recovery, from the Utilities menu click: Terminal

In Terminal:

cd '/Volumes/Macintosh HD/etc'
mv -v fstab fstat.bad
reboot

^{Note: the cd command above assumes the name of your normal Startup Disk is Macintosh HD. Change as necessary. You can see it by typing ls /Volumes. It will be the one similar to the one that has - Data in it.}

Directions for booting to safe mode and macOS Recovery:

To boot to safe mode:

Start up an Intel-based Mac in safe mode

1. On your Mac, choose Apple menu > Shut Down.
   After your Mac shuts down, wait 10 seconds.
   
2. Restart your Mac, then immediately press and hold the Shift key.
   
3. Release the Shift key when you see the login window.
   

^{From: Start up your Mac in safe mode}

To boot to macOS Recovery:

Start up your Intel-based Mac in macOS Recovery

1. Restart your Mac.
2. Immediately press and hold one of the following key combinations until you see the startup screen:
   

• Command-R: Start up from the built-in macOS Recovery System. Use this key combination to reinstall the latest macOS that was installed on your system, or to use the other apps in macOS Recovery.
  
• Option-Command-R: Start up from macOS Recovery over the internet. Use this key combination to reinstall macOS and upgrade to the latest version of macOS that’s compatible with your Mac.
  
• Option-Shift-Command-R: Start up from macOS Recovery over the internet. Use this key combination to reinstall the version of macOS that came with your Mac or the closest version that’s still available.
  

3. If you see a lock, enter the password for your Mac.
   
4. If you have multiple volumes on your disk, select the volume you want to recover, then click Next.
   
5. If requested, choose an administrator account, click Next, enter the password for the account, then click Continue.

^{From: Use macOS Recovery on an Intel-based Mac}