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Accepted
Jim
Asked: 2012-03-28 00:22:05 +0800 CST

Why is the port listed only in the specific format of netstat?

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I have Tomcat and I am trying to bind to 2 specific ports (using custom connectors). E.g. port A and port B.
Problem:
When I do netstat -a |grep A I do NOT see the port listed.
If I do netstat -antp I see both ports A and B listed.

What is the difference between the commands?

tomcat linux bash port netstat

2 Answers

  1. By specifying -n you tell netstat to use the port number instead of the service name. If you look at the output of netstat -a you will see that the port numbers are instead human-readable service names. These are mapped from /etc/services, so if you are listening on port 80 you will see *:http or hostname:http, and if you are listening on port 8080 you will see *:webcache or hostname:webcache.

    From the netstat man page on Fedora 16:

      --numeric , -n
       Show  numerical addresses instead of trying to determine symbolic host,
       port or user names.
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  2. Best Answer

    The -n option is the difference. Without it, netstat converts well-known ports such as 3306 and 80 into names such as mysql and http.

    If A is a well-known port and B isn't, only one of your ports will be listed by the first command.

    If a port is well-known, it should be listed in /etc/services.

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