How to enable MySQL slow query log

The slow query log consists of SQL statements that take more than long_query_time seconds to execute and require at least min_examined_row_limit rows to be examined.

The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization.

Here are the steps to enable MySQL slow query log permanently:

Login to server and edit MySQL configuration file 

vi  /etc/my.cnf

Add the following:

#Slow Query Log
#Log file
log-slow-queries = /var/log/slow-queries-log
#Logs queries longer than 2 sec
long_query_time = 2
#Logs queries not using indexes
log-queries-not-using-indexes TRUE

Change ownership of the log file /var/log/slow-queries-log to mysql for user and group.

chown mysql.mysql /var/log/slow-queries-log

Restart mysql

/etc/init.d/mysql restart