Linux Debugging

Enter Recovery Mode

If Linux isn't booting, you can enter recovery mode from grub itself: 

1. On boot, select "Advanced options for Ubuntu" 
2. Select "Ubuntu, with Linux []-generic (recovery mode)" where [] is the highest number (this is usually the 2nd option)
3. Now you have access to various recovery options; here are some of the relevant ones:
   1. resume - exits recovery mode
   2. clean - removes al leftover install files for currently installed problems (good to run if Linux isn't booting & storage might be a concern)
   3. dpkg - resumes incomplete program installs; use when something has been interrupted
   4. fsck - checks all file systems for errors & attempts to repair them
   5. networking - enables internet access
   6. root - enter terminal as root user

Basic Recovery Steps

From recovery mode, enable network and run clean, fsck, and dpkg. This will likely resolve most issues that are not related to faulty installs.

If the issue is a driver & isn't resolved by the other commands, enter the terminal as root & do the following:

apt-get autoremove
apt-get autoclean
apt-get update
apt-get -f install
apt-get dist-upgrade
apt-get upgrade

If NVIDIA drivers are the suspected source of the problem:

apt-get purge nvidia*
ubuntu-drivers autoinstall