edit /etc/my.cnf
using
# vi /etc/my.cnf
Then add
log-slow-queries
long_query_time = 5
Long_query_time is the number of seconds for a query to be considered long enough to log. The log will be created with detailed information about the queries that are slower than 5 seconds (in this case) for MySQL.
The default location of this log is
/var/lib/mysql/server-slow.log
