Changes to my.cnf don't take effect (Ubuntu 16.04, mysql 5.6)

Question

Changes I make to my.cnf don\'t seem to have any effect on the mysql environment. Here\'s a summary of what\'s happened...

I installed mysql 5.7 on Ubuntu 16.04 but

Answer 1

The config files are fine. The root cause is a bug in the MySQL 5.6 packaging for Ubuntu 16.04.

If you check your /var/log/syslog you'll probably see a line like this:

Sep 15 18:56:09 ip-172-31-18-162 kernel: [  383.840275] audit: type=1400 audit(1505501769.234:50): apparmor="DENIED" operation="open" profile="/usr/sbin/mysqld" name="/etc/mysql/my.cnf.fallback" pid=25701 comm="mysqld" requested_mask="r" denied_mask="r" fsuid=0 ouid=0

A security tool called AppArmor is denying access to a symlinked file (/etc/mysql/my.cnf.fallback).

Try this workaround, which will allow symlinks to be read by mysqld.

echo '/etc/mysql/** lr,' >> /etc/apparmor.d/local/usr.sbin.mysqld
systemctl reload apparmor

Now mysqld should see your custom config.

This bug appears to be fixed in the MySQL 5.7 Ubuntu package.

Answer 2

Obviously my.cnf.fallback is not the correct configuration file.

If you try this commands you can get output for possible my.cnf locations:

$ which mysqld
/usr/sbin/mysqld

$ /usr/sbin/mysqld --verbose --help | grep -A 1 "Default options"
Default options are read from the following files in the given order:
/etc/mysql/my.cnf ~/.my.cnf /usr/etc/my.cnf

It means mysql will check those locations for my.cnf file. Simply rename /etc/mysql/my.cnf.fallback as /etc/mysql/my.cnf:

mv /etc/mysql/my.cnf.fallback /etc/mysql/my.cnf