Cannot login in normal mode after security update (Ubuntu 20.04) 😤

Solution 1:

You can log into recovery mode through GRUB. From there, select the option to do system updates and then run the following commands:

sudo apt update
sudo apt dist-upgrade

If you run into an error, follow the instructions. Usually, the fix will be to run sudo apt -f install. If this doesn't fix the problem, the error message will tell you what else is wrong (usually a missing file or a dependency issue). If you have trouble interpreting the message, just post the error in your question (post a new question) and someone here should be able to know what to do.

Package management can seem overwhelming if you aren't familiar but 99.9% of the time you don't need to reinstall and the fix is quite simple.

Manually installing downloaded Nvidia drivers will cause the system to break every kernel update unless you reinstall the driver after each new kernel. However, the proprietary Nvidia drivers are available through the main and Universe repositories using apt so there's no need to manually install.

You can automatically select/install the proprietary Nvidia drivers using the following commands:

sudo apt update
sudo ubuntu-drivers autoinstall

You can also disable automatic updates so that if there is a problem, you can always deal with it directly and know exactly what's going on.

To disable automatic updates, run the following command to edit a file (NOTE: you will need to run sudo apt update and sudo apt dist-upgrade daily to keep your system up to date):

nano /etc/apt/apt.conf.d/20auto-upgrades

Edit the file to contain only the following lines:

APT::Periodic::Update-Package-Lists "0";
APT::Periodic::Download-Upgradeable-Packages "0";
APT::Periodic::AutocleanInterval "0";
APT::Periodic::Unattended-Upgrade "0";

After you are done editing, press CTRL+o to save the changes and then press CTRL+x to exit nano.

Lastly, if and when a kernel update causes problems, you can log in to an older kernel through your GRUB menu.