During installation , Oracle Universal Installer assigns port numbers to components from a set of default port numbers. Many Oracle Database components and services use ports. As an administrator , it is important to know the port numbers used by these services, and to make sure that the same port number is not used by two services on our host .
I.) Is the port used by another Oracle Database installation on the host?
The installation may be up or down at the time; Oracle Database can still detect if the port is used.
This could be any process on the host, even a non-Oracle Database process.
If we change a port number, it is not updated in the portlist.ini file, so we can only rely on this file immediately after installation. if we want to see all the different port numbers click on Different Port Numbers.