I have often suffered this painful thing.When I start a service but the destination port is always used.So I should list all open ports and kill the occupied application.
So This is a short tip for how to list open ports on Linux

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sudo netstat -tulpn

Note sometimes you should grant the command for a enough access.
For a better understanding,please

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man netstat

or navigate to http://linux.about.com/od/commands/l/blcmdl8_netstat.htm

For Mac Users

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sudo lsof -i -P | grep -i "listen"

Others

• UNIX and Linux System Administration Handbook