How to view all the open ports

By | January 28, 2014

RadarOne of the first thing you learn as a system administrator is that programs (applications, scripts) need TCP connections to communicate with other devices. This can sometimes also be a problem. Some exploits open a new port and can cause some serious problems.

However, there is a very simple way to find out which programs opened TCP ports on your machine:

netstat -tlnp

You may see that some ports are open on 0.0.0.0 – this means they are listening on ALL network interfaces.

Other applications are listening only on 127.0.0.1 – this means they accept connections only from the local machine.

As a general principle, you should limit the access only to the networks which are required.

[[email protected] ~]# netstat -tlnp

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address       Foreign Address  State       PID/Program name
tcp        0      0 0.0.0.0:22          0.0.0.0:*        LISTEN      5349/sshd
tcp        0      0 127.0.0.1:953       0.0.0.0:*        LISTEN      3959/named
tcp        0      0 0.0.0.0:25          0.0.0.0:*        LISTEN      2773/smtpd
tcp        0      0 0.0.0.0:443         0.0.0.0:*        LISTEN      16507/nginx
tcp        0      0 127.0.0.1:199       0.0.0.0:*        LISTEN      20722/snmpd
tcp        0      0 127.0.0.1:9000      0.0.0.0:*        LISTEN      2363/php-fpm
tcp        0      0 0.0.0.0:21          0.0.0.0:*        LISTEN      28984/vsftpd
tcp        0      0 0.0.0.0:80          0.0.0.0:*        LISTEN      16507/nginx
tcp        0      0 108.166.185.123:53  0.0.0.0:*        LISTEN      3959/named
tcp        0      0 127.0.0.1:53        0.0.0.0:*        LISTEN      3959/named
tcp        0      0 :::22               :::*             LISTEN      5349/sshd
tcp        0      0 ::1:953             :::*             LISTEN      3959/named
tcp        0      0 :::3306             :::*             LISTEN      31184/mysqld
tcp        0      0 :::8080             :::*             LISTEN      19340/httpd

Yes, I know, not very intuitive, but trust me, it is very powerful.

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