Ubuntu is FOG's enemy
Tom Elliott SENIOR DEVELOPER 2017. ápr. 29. 3:17
TLDR; Rerun the fog installer if you have lost “Database Connectivity” to your fog server, or run the ALTER USER syntax shown below.

So Ubuntu 16, among others I suppose, enable a “security updates” to be applied automatically as a “default” to things. Why, well it makes it simpler to ensure your Ubuntu systems are in compliance and patched for any potential exploits. This causes unknown and unexpected issues.

I figured it’d be a safe thing to express that there could be problems (as many of you have already experienced) that when these updates go up (with or without your knowledge) it can break functionality in unexpected and inopportune ways.

The quickest fix is to simply rerun the fog installer which should correct the problem.

As a note, it seems this problem is specific only when the mysql account is the 'root' user AND the password is blank.

The “fix” if you must do it manually is to open a terminal and obtain root:
Super (Windows Key) + T then sudo -i (in most cases).

From there, open mysql with mysql -u root

NOTE: MySQL MUST be run with ROOT.

Run:

ALTER USER 'root'@'127.0.0.1' IDENTIFIED WITH mysql_native_password BY ''; AND
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '';

It’s okay if one of them fails. This is going to fix Most people’s issues.

I would highly recommend removing the unattended-upgrades as many of these “sudden” issues came as a security patch ubuntu pushed out. By default Ubuntu typically set’s this for you as enabled and it can cause havoc on you as you (the admin) may not have “done” anything.

To prevent this problem from happening in the future you could run:

apt-get -y remove unattended-upgrades (AS Root again).

https://forums.fogproject.org/topic/10006/ubuntu-is-fog-s-enemy