This is considered good practice for any linux platform that has publicly addressable interfaces... Of course you will need to setup PKI public/private keys for any secure login. I am not suggesting that you turn off authentication entirely !
I had a VPS linux host out there untended for a while, and the hackers find it irresistible - there were 11,000+ authentication failures in the logs.

To stop password authentication by sshd, just add these entries to your /etc/sh/sshd_config file:

Please note that if you haven't changed over to MariaDB - you should ... But more to the point for this post - if you need to reset your root mysql or mariadb password, the easiest way to do it on an Ubuntu platform is to run the following commands: First, you need to know what version of mysql or MariaDB you have, so run this to search for the package name: root@bazingah:/usr/local/bin# dpkg-query -S mariadb-server

Say you want to change the character_set or collation of a MariaDB (MySQL) DB:

ALTER DATABASE databasename CHARACTER SET utf8 COLLATE utf8_general_ci;

I see this fairly often when I have done fast installs of ubuntu:
"Connection for controluser as defined in your configuration failed."

What happens is I ignore the install script that needs to run for PhpMyAdmin to establish its database etc.
Happily the fix is fairly easy - just run the script again now:
sudo dpkg-reconfigure phpmyadmin

I am surprised that there have been no updates to the webmin interface to support the new samba version (that has been rolled out to most major linux distros now) -- am I the only one that has been using webmin to do my admin on samba servers ? I think NOT...

Anyway - here is a quick and dirty fix to the start/stop entries in the webmin samba module to correct it for Version 4:

Command to stop Samba servers
service smbd stop && service nmbd stop

Command to start Samba servers
service smbd start && service nmbd start

Beware people (like me) who offer solutions (like this)...

That said, here is how I have (several times) repaired this error on my HTC EVO 4G LTE.
(it's a Sprint phone, but I think these issues are across all of the telcos)

On your KEYPAD, type this:

Polymer looks like it may be very cool -
https://www.youtube.com/watch?v=yRbOSdAe_JU

I was excited to find this, so I am saving it here.

To change an smb passwd in a bash script:

echo -e "newpasswd\nnewpasswd" | (smbpasswd -s username)

And note the "\n" in there to push a newline between the two passwords...

For the unix (Linux) username:

echo -e "newpass\nnewpass" | (passwd --stdin username)

I have been building a new web server platform and tried to install drush using pear as I have in the past, but it is not NOT the recommended way to install it any longer (who knew?).
Drush has developed a huge cult following for it's ease of use in maintaining multiple drupal based sites very easily from the CLI. I cannot recommend drush highly enough - I can update the code for all of my sites in a few minutes - back in the gory days it would take me ages to do that... These steps worked flawlessly for me on Ubuntu 14.04 today.