How to enable MariaDB/MySQL logs ?

As a web developer that have been toying with MySQL/MariaDB for more than 5 years. I can tell you that the best way to start debugging your application or looking for ways to improve database performance is to enable the logs. To enable the MySQL/MariaDB logs :

Edit MySQL configuration file:

vi /etc/mysql/my.cnf

Note : Depending on your installation, the my.cnf file could be located on different directory. MariaDB's my.cnf is located at /etc/my.cnf

Slow Query Log

To enable Slow Query Log, add these lines or uncomment these two lines. Change the destination location for the log files if you prefer.

logslowqueries = /var/log/mysql/mysql-slow.log

longquerytime = 2

log-queries-not-using-indexes

To enable Error Log, add these lines or uncomment these two lines. Change the destination location for the log files if you prefer.

[mysqld_safe]

logerror=/var/log/mysql/mysqlerror.log

[mysqld]

logerror=/var/log/mysql/mysqlerror.log

To enable General Query Log, add these lines or uncomment these two lines. Change the destination location for the log files if you prefer.

generallogfile = /var/log/mysql/mysql.log general_log = 1

To enable these changes, restart mysql

sudo /etc/init.d/mysql restart

or

sudo service mysql restart

References :

http://dev.mysql.com/doc/refman/5.7/en/slow-query-log.html

http://dev.mysql.com/doc/refman/5.7/en/error-log.html

http://dev.mysql.com/doc/refman/5.7/en/query-log.html