macOS Catalina 10.15: Black screen or only one monitor is working after upgrade

This issue might occur after upgrading from macOS Mojave to macOS Catalina.

The user will see a black screen or single functioning DisplayLink device, despite the fact that two of them are plugged-in and both are visible in macOS Display Preferences.

 

In order to fix this problem please perform the following steps:

1. Uninstall DisplayLink Software

2. Go to the macOS Recovery Mode.

macOS Recovery is part of the built-in recovery system of your Mac. You can start up from macOS Recovery and use its utilities to recover from certain software issues or take other actions on your Mac.

How to enter macOS Recovery Mode

1. Turn on your Mac and immediately press and hold Command (⌘)-R.
2. Release the keys when you an Apple logo, spinning globe, or other startup screen.
3. You might be prompted to enter the login password of an administrator of this Mac, or your Apple ID password, or a firmware password. Enter the requested password to continue.
4. Startup is complete when you see the utilities window:
This is the Apple's tutorial providing more info on macOS Recovery Mode -> https://support.apple.com/en-us/HT201314

3. Run the "Disk Utility" application from the window with applications selection by clicking on it


4. You should then see this Window



5. If you have FileVault enabled, or if for any reason the first internal drive is not mounted please mount it.


1. The first internal drive in our case is (on the left top) Internal: "Macintosh HD"
2. If there is active button with name "Mount" - please click on it and if needed - enter your password
3. if there is active button with name "Unmount" - no action needed
4. Please write the name of your drive somewhere on the paper or note - it will be needed in next steps. In this case it is: "Macintosh HD".

6. Please close the application "Disk Utility" by clicking on the red button in the top left corner of the Disk Utility windows - just as normal as you're closing the application.


7. Please run "Terminal" Application from the Top Menu Bar.


1. Please navigate to the top menu bar 
2. Select "Utilities" 
3. Then run "Terminal" by clicking on it


 

8. You should then see Terminal application window


9. Now, it's time to execute single command which help to rebuild the system cache, which is a cause of the issue


The command is: 
kextcache -i "/Volumes/<VolumeName>"

Where <VolumeName" is your disk name. It is the same name we've checked in Disk Utility step 4

So in this case the final command is: kextcache -i "/Volumes/Macintosh HD"

Please write it in the terminal application and press <Enter> key on the keyboard


10. After few seconds you should see similar output



It is OK when you see the last line with KernelCache ID.

11. Select "Reboot" from the top left menu - the menu with "Apple" icon. 

12.    Install DisplayLink Software again.

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