Access denied for user 'root'@'localhost' (using password: NO) on 'service mysql start'

Question

OS

$ uname -a
Linux aurora 4.4.0-59-generic #80-Ubuntu SMP Fri Jan 6 17:47:47 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

MySQL

$ mysqladmin --version
mysqladmin  Ver 8.42 Distrib 5.7.16, for Linux on x86_64

Clearly something is trying to log into my mysql server as root upon

service mysql start

but I don't know what it is.

The last line in /var/log/mysql/error.log related to starting the server is:

[Note] Access denied for user 'root'@'localhost' (using password: NO)

How do I figure the offending config file or server or application that is trying to log in as 'root'@'localhost' on startup? What other information can I provide to help to understand and resolve this issue?

Also, I am able to log in as 'root'@'localhost' if I do so explicitly. It's only the [Note] in the error log that is irritating me and that I want to debug.

Answer 1

This is because the mysqladmin cannot login as root.

The guilty is this Systemd unit:

/lib/systemd/system/mysql.service

Which executes this command to see if the daemon is started properly:

ExecStartPost=/usr/share/mysql/mysql-systemd-start post

Which executes:

# mysqladmin ping         
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'root'@'localhost' (using password: NO)'
# echo $?
0

The return value is 0 despite the error message so the daemon is marked as started.

Debian has a file which contains an user to execute unattended operations, to use this file explicitly the previous command must be executed in this manner:

mysqladmin --defaults-file=/etc/mysql/debian.cnf ping

After this explanation I can ignore the line in the error log.