How to make modifications work without restarting MySQL?

I deleted the slow.log of MySQL,but seems it's still cached in the system.

But I don't want to restart MySQL.

From serverfault apache

• Have you tried flush logs;? Flush logs "closes and reopens all log files."

  apache : Is this command the same as `apachectl graceful` of Apache?

  Warner : It doesn't restart MySQL. It closes and reopens the log files.

  apache : What if I made some change in `my.cnf`,how to make it work without restarting MySQL?

  Warner : Some changes can be made dynamically with `set variable`, others can't be changed without a restart. See: http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html
  From Warner