title: What is CSlistener and why is it running on port 9000 on my mac and restarts itself every time I stop it
body: <p>Context:
  Woke up and couldn't start my app that uses port <code>9000</code> because address was already in use. Message on my terminal is</p>
  <pre><code>Error response from daemon: Ports are not available: listen tcp 0.0.0.0:9000: bind: address already in use
  </code></pre>
  <p>The command <code>netstat -anvp tcp | awk 'NR&lt;3 || /LISTEN/'</code> lists a process running on port 9000 like;</p>
  <pre><code>Active Internet connections (including servers)
  Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)     rhiwat shiwat    pid   epid  state    options
  tcp4       0      0  127.0.0.1.9000         *.*                    LISTEN      131072 131072   1260      0 0x0080 0x00000006
  tcp4       0      0  127.0.0.1.3306         *.*                    LISTEN      131072 131072    997      0 0x0100 0x00000006
  tcp4       0      0  127.0.0.1.33060        *.*                    LISTEN      131072 131072    997      0 0x0000 0x00000006
  </code></pre>
  <p>there are more processes listed, i just trimmed it. I can see stuff like <code>127.0.0.1.3306</code> which i think is mysql, thats fine, but the process running at <code>127.0.0.1.9000</code> is what am not sure about.
  Killing the process with <code>sudo kill 1260</code>, the ID of the process is <code>1260</code> and running the command <code>netstat -anvp tcp | awk 'NR&lt;3 || /LISTEN/'</code> lists the process again with a different process ID.</p>
  <p>Running <code>sudo lsof -i TCP:9000</code> prints</p>
  <pre><code>php-fpm 2997 root    9u  IPv4 0xf6c73412e60c41cb      0t0  TCP localhost:cslistener (LISTEN)
  php-fpm 3000 _www   10u  IPv4 0xf6c73412e60c41cb      0t0  TCP localhost:cslistener (LISTEN)
  php-fpm 3001 _www   10u  IPv4 0xf6c73412e60c41cb      0t0  TCP localhost:cslistener (LISTEN)
  </code></pre>
  <p>So after seeing this printed I googled <code>cslistener</code>, notice that there is a string <code>TCP localhost:cslistener</code> in what's printed.</p>
  <p>One find suggested looking for it in the file <code>/etc/services</code> and sure I found it, the lines looked like</p>
  <pre><code>...
  cslistener      9000/udp     # CSlistener
  cslistener      9000/tcp     # CSlistener
  ...
  </code></pre>
  <p>So, my question is, what is <code>cslistener</code> and why is it running on port 9000 and restarting itself everytime i kill it.</p>