The web UI for Zabbix shows the Zabbix server is not running. In "Status of Zabbix" there is a parameter "Zabbix server is running" and it has a value of "No." To investigate on the back-end of the Zabbix server you run this command: tail -f /var/log/zabbix/zabbix_server.log
You see this error: "Access denied for user 'zabbix'@'localhost' (using password: YES)"
What should you do?
Examine the zabbix_server.conf file. Run this command: sudo vi /etc/zabbix/zabbix_server.conf
Verify the DBName=, DBUser, and DBPassword stanzas. Typos in these assignments or if one is commented out could cause the problem you encountered. Beware of near matches like "zabbix" and not "zabbixdb" or "zabbixuser". Incorrect info in this file could cause the error you are seeing.