You may want to change the password of SYSMAN user time to time because of security policies. OMS uses sysman account to login into the repository DB and if there is a mismatch in the password at the DB level and the configuration files, the OMS cannot start and function properly. So whenever you change the password of SYSMAN on the repository database of EM Grid Control, you need to update the configuration files.
Before 10.2.0.5, this was a manual process. You should stopp all the agent monitoring the Repository DB and the OMS instances that are associated with the repository:
emctl stop agent
Then you enter the password into the emoms.properties by changing the following lines: