How to boot into recovery mode in Ubuntu?

Issue

The Caldera PC no longer starts.

Problem

Potentially full disk.

Solution

1. Before you begin, if any error messages appear on the screen, consider taking a photo of them. This will allow you to provide the images to your IT department or technical support if needed, especially if the following process does not resolve the issue.
   
   
2. Restart your computer.
   
   
3. Before the boot splash screen appears, press the Shift or Esc key (it could be another key, as it depends on the laptop's manufacturer) to enter the GRUB boot menu.
   
   

4. After you are in the GRUB boot menu, select Advanced options for Ubuntu:
   
   
   

5. In the advanced options, select a recovery mode.
   
   
   
6. Wait till you get to the Recovery Menu:
   
   
   
7. In the Recovery Menu, you will find a few recovery options for your system:
   

   resume	Boots normally to your main OS.
   clean	This option cleans your OS and removes obsoleted and unnecessary packages.
   dpkg	Tries to fix package manager issues.
   failsafeX	Starts the system in Safe graphics mode.
   fsck	Checks errors in the file system. This option won't work in recent Ubuntu systems as the disk is mounted.
   grub	Updates the GRUB boot loader (sudo update-grub)
   network	Enables Wi-Fi and network services.
   root	Drops you to a root prompt to execute commands as the root user.
   system-summary	Shows information about your system.

8. Choose the root option to access the shell where you will be able to type command lines.