Mariadb Sovle : Plugin 'unix_socket' is not loaded

The "unix_socket" has been called by mysql authentication process (maybe related to a partial migration of database to mariadb, now removed). To get all stuff back working go su:

sudo su

then follow:

/etc/init.d/mysql stop
mysqld_safe --skip-grant-tables &
mysql -uroot

This will completely stop mysql, bypass user authentication (no password needed) and connect to mysql with user "root".

Now, in mysql console, go using mysql administrative db:

use mysql;

To reset root password to mynewpassword (change it at your wish), just to be sure of it:

update user set password=PASSWORD("mynewpassword") where User='root';

And this one will overwrite authentication method, remove the unix_socket request (and everything else), restoring a normal and working password method:

update user set plugin="mysql_native_password";

Exit mysql console:

quit;

Stop and start everything related to mysql:

/etc/init.d/mysql stop
kill -9 $(pgrep mysql)
/etc/init.d/mysql start

Don't forget to exit the su mode.

Now mySQL server is up and running. You can login it with root:

mysql -u root -p

or whatever you wish. Password usage is operative.