In newer versions of Linux it’s not easily possible to just move the MySQL data directory to another location and modify my.cnf or create a symbolic link. There is a secutity/protection “daemon” running in background checking which locations is some process trying to access. If it’s allowed, then access is granted, otherwise the process is unable to read/write the required data. This guardian is called “APPARMOR”
I wanted to move the MySQL data directory (among others, like /var/www, git projects repositories, owncloud data directory, media like photos, videos, music, …) to another location on my file system due to separation of data from the rest of the running system – in case of failure I’d just re-install the system, but data stored on separated partition will remain untouched and can just be binded/mounted to the fresh installed system.
Let’s assume I’ve my data partition mounted as /mnt/data. So I moved the MySQL data directory there using:
sudo mv /var/lib/mysql /mnt/data
And created a symbolic link on original location
cd /var/lib sudo ln -s /mnt/data/mysql
When I tried to start MySQL server daemon I got the following error message:
start: Job failed to start
So I edited the Apparmor configuration alias file for MySQL:
sudo nano /etc/apparmor.d/tunables/alias
with the following content:
... alias /var/lib/mysql/ -> /backup/mysql/, ...
and reloaded the configuration using command
sudo /etc/init.d/apparmor reload
Now the MySQL server should be started correctly
mysql start/running, process 27288