How to Close open Ports manually in Ubuntu / Linux

By | April 30, 2023

Open ports

When running any kind of server application like http or ftp server, or doing socket programming, it might so happen that a server program when recompiled/rerun fails to bind to a particular port number because that port number is already in use.

In such a case, you can either restart the system or close the port manually.

To close the port number manually first the process name/id has to be found out that is holding the port open and then use the kill command on that process.

Find pid with lsof - The lsof command can be used to find the pid and command name of the program or application that is currently using the port. Here is a quick example:

$ lsof -i :8888
java    8461 enlightened   11u  IPv6 138527      0t0  UDP *:8888

In the above example it is seen that port 8888 is being held in use by the command java with pid 8461. Now kill the process by doing any of the following

$ kill 8461
$ killall -9 8461
$ killall -9 java

Find process/pid with netstat - The netstat command can also be used to find out which process is holding a certain port number

$ netstat -u -ap
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
udp        0      0 *:18347                 *:*                                 -               
udp        0      0 localhost:11211         *:*                                 -               
udp        0      0 localhost:36254         localhost:36254         ESTABLISHED -               
udp        0      0 localhost:domain        *:*                                 -               
udp        0      0 *:ipp                   *:*                                 -               
udp        0      0 *:42038                 *:*                                 -               
udp        0      0 *:17500                 *:*                                 4090/dropbox    
udp        0      0 *:mdns                  *:*                                 -               
udp        0      0 localhost:58797         localhost:7777          ESTABLISHED 9831/ncat       
udp        0      0 localhost:42724         localhost:domain        ESTABLISHED -               
udp6       0      0 [::]:46282              [::]:*                              -               
udp6       0      0 [::]:mdns               [::]:*                              -               
udp6       0      0 [::]:9999               [::]:*                              11598/java

The port we want to close here is 9999. And netstat shows that the pid is "11598" and command name is "java". Over here we used the -u for udp port. If its a tcp port then the "-u" switch is not needed.

To make the search process easier, simply pipe the output of netstat to grep and look for the exact port number

$ sudo netstat -ap | grep :9050
tcp        0      0 localhost:9050          *:*                     LISTEN      1613/tor

Once the process id/name is found end it with the kill command.

$ kill 11598

Find pid with fuser - This is yet another command to find the pid/process holding a certain port number. The sytanx is as follows:

fuser -k -n protocol portno

Quick example

$ fuser -k -n udp 7777
7777/udp:            11774


The above examples show how to find specific process and its pid that are using a given port number. Once you know the port number you can just kill that process and free the port.

Note that if the process was initially launched with root privileges then you would need root privileges to kill it as well.

About Silver Moon

A Tech Enthusiast, Blogger, Linux Fan and a Software Developer. Writes about Computer hardware, Linux and Open Source software and coding in Python, Php and Javascript. He can be reached at [email protected].

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