Comments - Spurious - "Access denied for user 'root'@'localhost' (using password: NO)" in the /var/log/mysql/error.log.1 file
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Base on an internet search, the error message is "linked" to the existence of a user "debian-sys-maint". See the Ask Ubuntu question "error running shared postrotate script for mysql". No such user exists on my installation of MariaDB.
https://askubuntu.com/questions/1252340/error-running-shared-postrotate-script-for-mysql
I created a user "debian-sys-maint" and will have to wait to see if the issue is now resolved.