Linux (Ubuntu)
Please read “Security” section of the manual to find out how to run mysqld as root!
by admin on Jun.26, 2018, under Linux (Ubuntu)
This means you’re trying to run mysql as the root User which is not recommended at all, due to security reasons.
If you’d like to do so anyways, solely for testing purposes, you can edit /etc/my.cnf (or create the file, if it doesn’t exist) and apply the following configuration:
[mysqld] user=root
Never use this on a production environment.