Outages can cause file system inconsistency and will result in a VM booting into Read Only state.
To correct the issue, a file system check must be ran for the system to boot normally again.
Step 1: Boot into the Grub Menu loader.
Tips: holding down the SHIFT key while the system is booting up or repeatedly hit the ESC key should bring up the Grub Menu.
From the Grub Menu, go to Advanced Options.
Step 2: Select the first Recovery mode available from the list.
Step 3: Select "fsck" from the menu options to run a file system check.
Step 4: Select "Yes" to mount the disk as Read/Write.
Sample Output of the system doing it's check. For any prompts that may show up, select "Y"es to fix the issues.
You should run the "fsck" twice to make sure no further errors show up and system will be a be to boot normally again.
Step 5: Select "Resume" to boot system again.