OEM and common troubleshooting

1. oem: oracle enterprise manager, which is a graphical management tool for oracle, port number 1158, use https://address:1158/em to access
the default installation when installing the database, you can use the emca command to rebuild
2. There are two versions : database control is used to monitor a single database
grid control is used to manage large-scale and complex environments with multiple databases
3. Start and close oem and view the status: emctl start|stop|status dbconsole
4. The oem interface consists of the main directory, performance, availability, Servers, solutions, data movement, software and support components