How to roll Introscope Enterprise Manager Log files including EM.log based on date and size?
Application Performance Management from 10.7
Please note that by rolling over the logs at a smaller size, any problem that comes up may be overwritten quickly. So please keep this in mind, should you encounter an issue that you need to be troubleshooted, its best to temporarily increase the log file size so that CA Support can quickly ascertain the situation.
See links below for more information: