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I recently tried to upgrade my laptop from 16.04 LTS to 18.04 LTS. The upgradation process was smooth; but when I try to log in, it is showing an Authentication Error

Authentication Error

and then I get this black screen which stays indefinitely

boot messages

I am a rookie in these regards, so a step-by-step guide will be much helpful. Thanks in advance.

Results after trying suggestions by Manu Mathur:

sudo apt-get update gives this:

no internet

sudo apt-get upgrade gives this:

nothing to do

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2 Answers 2

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Had similar problem upgrading from 14.04 to 16.04. Logged to TTY and did a shutdown, which lead to other problem. Could log in to TTY anyway (CTRL+ALT+F1). Then I ran:

sudo dpkg --configure -a
sudo apt-get update
sudo apt-get upgrade
sudo reboot

Helped in my case. Solution is based on a related earlier answer. Configuring did the trick.

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I guess one of these two solutions can help you:

Solution - I

  • Try logging in the TTY mode.
  • If you can log in, this means your password is correct. Post login, use the command: sudo apt-get update and sudo apt-get upgrade.
  • If you do not like GNOME on Ubuntu you can go back to the Unity.

How to Login into TTY mode?

  • To access TTY, use this combination:

To access them, use either of these keys combination: use Ctrl + Alt + F1 keys(or you can also try use Ctrl + Alt + F3 on 17.10 and newer versions)

Note: You can change the keys from F1 to F1 - F6 to access the terminal that you want)

  • If you wish to get back to your GUI session (the normal desktop), try these key combinations:

Ctrl + Alt + F7 keys (or F2 on 17.10 and newer)

Solution - II

My second guess is that you might have some broken packages. To check, do the following:

  • Switch to a TTY mode, example: use Ctrl + Alt + F3 keys, and login to the command line
  • Once you are in the command line, run the command: sudo apt install -f and see if that helps

P.S. If you own a "Dell" laptop, then see if you have AMDGPU-pro driver installed. It is also known to conflict with the upgrade process. If you find it, just remove it using the "TTY" command.

Keep us posted via the comments section.

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  • Please instruct how to login in TTY mode. Mar 15, 2019 at 18:30
  • I have included the process between the two solutions @SubhajitPaul. Mar 15, 2019 at 18:38
  • I am editing my question with the snapshots to show you the results of your suggestions. Mar 15, 2019 at 18:48
  • That would be great. Thank you. Mar 15, 2019 at 18:51

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