enable mysql slow query log in my.cnf

Step 1:  add following two line under mysqld

[mysqld]

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

long_query_time = 10

step 2: create an empty log file and chage the owner

  vim /var/log/mysql-slow.log

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

step 3: reboot mysql

  /etc/init.d/mysqld stop

  /etc/init.d/mysqld start