Linux on Lightsail instance is asking for a password and it's not working

I'm trying to restart mariaDB on Ubuntu but it's not letting me.

I enter:

systemctl restart mariadb

and get:

==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===

Authentication is required to restart 'mariadb.service'.

Authenticating as: Ubuntu (ubuntu)

Password: 

polkit-agent-helper-1: pam_authenticate failed: Authentication failure

==== AUTHENTICATION FAILED ===

I have the same password for all functions so I do not understand why it is not working. What can I do?

How many English words
do you know?
Test your English vocabulary size, and measure
how many words do you know
Online Test
Powered by Examplum