10 Netstat Command Examples in Linux

Author - Sanjay

Introduction

Netstat is one of the most used command for checking and monitoring network configurations , iptables and routing informations. Let's take out the 10 most practical examples used commonly in day to day system admin job.

Introduction
Pre-Requisistes
List All Connections With Ports
List All Sockets With LISTEN state in Server
Show the statistics TCP, UDP protocol

Pre-Requisistes

A CentOS/RHEL 7 production server or a Linux VPS with netstat utility installed working on your server.

List All Connections With Ports

If you want to list down all the listening and non listening ports , you can do as shown below

netstat -a | more

output :-

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 0.0.0.0:pop3            0.0.0.0:*               LISTEN
tcp        0      0 localhost.localdoma:783 0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:imap            0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:sunrpc          0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:http            0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:urd             0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:domain          0.0.0.0:*               LISTEN
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  3      [ ]         DGRAM                    9477     /run/systemd/notify
unix  2      [ ]         DGRAM                    15622    /var/run/chrony/chronyd.sock
unix  2      [ ]         DGRAM                    9479     /run/systemd/cgroups-agent

Once you press enter it shows more items in the list .

Find All TCP Ports

In above example we have listen down all the ports but lets say i only need to find TCP ports used in my server. Lets see how we can do that .

netstat -at

output :-

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 0.0.0.0:pop3            0.0.0.0:*               LISTEN
tcp        0      0 localhost.localdoma:783 0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:imap            0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:sunrpc          0.0.0.0:*               LISTEN

Find All UDP Ports

If we want to list down all UDP ports opened and listened in my server we can run the below command

netstat -au

Output :- image info

List All Sockets With LISTEN state in Server

If you are only concerned with all ports and wan to know all listen ports use -l option . Along with this if you want to list down all TCP ports which are in LISTEN state use -lt . For getting UDP Ports which are in LISTEN state use -lu .