mysql> show variables like '%log%';
Recreate the log files I deleted by mistake. It appears the MySQL does not recreate them automatically.
touch /var/log/mysql.log
chown mysql:adm /var/log/mysql.log
touch /var/log/mysql/error.log
chown mysql:adm /var/log/mysql/error.log
touch /var/log/mysql/mysql-slow.log
chown mysql:adm /var/log/mysql/mysql-slow.log
touch /var/log/mysql/mysql.log
chown mysql:adm /var/log/mysql/mysql.log