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.

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
slow_query_log = 1
slow_query_log_file = /var/log/mysql/slow.log
# Log queries longer than 2 seconds
long_query_time = 2
# Log queries not using indexes
log_queries_not_using_indexes = 1

Create the log directory and give it to the database user:

mkdir -p /var/log/mysql && chown mysql:mysql /var/log/mysql

Restart the database server (MariaDB shown; use mysqld on MySQL). To switch the log on without a restart, run SET GLOBAL slow_query_log = 1; as well.

systemctl restart mariadb