MySQL is a widely used and fast SQL database server. It is a client/server implementation that consists of a server daemon (mysqld) and many different client programs/libraries.

Mysql data directory is important part where all the mysql databases storage location.By default MySQL data default directory located in /var/lib/mysql.If you are running out of space in /var partition you need to move this to some other location.

Note:- This is only for advanced users and before moving default directory make a backup of your mysal databases.

First you should stop the mysql server. e.g.

 # /etc/init.d/mysql stop

After that you should copy the old data directory (e.g. /var/lib/mysql) incl. privileges to your new directory via

 # cp -R -p /var/lib/mysql /new/data/dir

now you can change in /etc/mysql/my.cnf the data new and restart the server

 # /etc/init.d/mysql restart

You have to copy the database when the server is not running.