How To Use Linux SS Command

Introduction

The ss (socket statistics) tool is a CLI command used to show network statistics. The ss command is a simpler and faster version of the now obsolete netstat command. Together with the ip command, ss is essential for gathering network information and troubleshooting network issues.

This article gives an overview of how to use the ss command and shows examples of the most common use cases.

How to Use the ss Command in Linux

Prerequisites

  • Access to a terminal or command line
  • Installed iproute2 software package

Note: Use the apt-get commands to install, update or upgrade the iproute2 software package.


Linux ss Command Examples

The basic ss command usage is without any parameters:

ss

The output returns a list of open non-listening sockets with established connections.

Terminal output of the command ss

The columns show the following details:

  • Netid – Type of socket. Common types are TCP, UDP, u_str (Unix stream), and u_seq (Unix sequence).
  • State – State of the socket. Most commonly ESTAB (established), UNCONN (unconnected), LISTEN (listening).
  • Recv-Q – Number of received packets in the queue.
  • Send-Q – Number of sent packets in the queue.
  • Local address:port – Address of local machine and port.
  • Peer address:port – Address of remote machine and port.

For a more detailed output, add options to the ss command:

ss <options>

Or list the options individually:

ss <option 1> <option 2> <option 3>

Note: There are many Linux CLI tools for testing the network speed if the connection is slow.


List All Connections

List all listening and non-listening connections with:

ss -a

Or:

ss --all

Terminal output of the command ss -a command

List Listening Sockets

To display only listening sockets, which are omitted by default, use:

ss -l

Or:

ss --listen

Terminal output of the command ss -l

List TCP Connections

To list TCP connections, add the -t option to the ss command:

ss -t

Alternatively:

ss --tcp

Terminal output of the command ss -t

List All TCP Connections

Combine the options -a and -t with the ss command to output a list of all the TCP connections:

ss -at

Terminal output of the command ss -at

List All Listening TCP Connections

Combine the options -l and -t with the ss command to list all listening TCP connections:

ss -lt

Terminal output of the command ss -lt

List UDP Connections

To show a list of UDP connections, use:

ss -u

Or:

ss --udp

Terminal output of the command ss -u

List All UDP Connections

Combining the options -a and -u with ss outputs a list of all the TCP connections:

ss -au

Terminal output of the command ss -au

List All Listening UDP Connections

To list all listening UDP connections, use the ss command with options -l and -u:

ss -lu

Terminal output of the command ss -lu

List Unix Sockets

To show all the Unix family sockets, use:

ss -f unix

Or use the shorter alias:

ss -x

Terminal output of the command ss -x

List Raw Sockets

To list raw sockets, use:

ss -w

Or alternatively:

ss --raw

List Connections to a Specific IP Address

List connections to a specific destination IP address with:

ss dst <address>

For example:

ss dst 104.21.3.132

Terminal output of the command ss dst address
To show connections to a specific source address, use:

ss src <addresss>

For example:

ss src 192.168.100.2

Terminal output of the command ss src address


Note: To show all connections to the local machine, check your IP address and add the ss src command.


Check Process IDs

To show process IDs (PID), use:

ss -p

Terminal output of the command ss -p

List Summary Statistics

List the summary statistics for connections with:

ss -s

Terminal output of the command ss -s

List IPv4 and IPv6 Socket Connections

Filter results further by listing IPv4/IPv6 connections with:

ss -4

Or:

ss -6

For example, list all IPv6 UDP connections with:

ss -au6

Terminal output of the command ss -au6

Filter Connections

The ss command allows advanced filtering of results and searching for specific ports or TCP states.

Filter Using TCP States

Filter TCP connections using the TCP predefined states:

ss state <name of state>

For example, to find all listening TCP connections:

ss -t state listening

Terminal output of the command ss -t state listening

Filter by Port Number

Filter for a specific destination port number or port name:

ss <options> dst :<port number or name>

For example:

ss dst :5228

Terminal output of the command ss dst port number

Or use a port name:

ss dst :https

Terminal output of the command ss dst port name
Combine multiple queries for more advanced filtering. For example, find all connections with a destination port 5228 or source port mysql:

ss -a dst :5228 or src :mysql

Terminal output of the command ss command advanced search

Check Man Pages or List All Commands

Check the manual page of ss in the terminal for a detailed overview of how to use the command:

man ss

For a quick overview of the available options, enter:

ss -h

netstat VS ss Command

The ss command is considered a replacement command for the obsolete netstat. The speed and better filtering options of CLI utilities from the iproute2 software package are preferable to the net-tools software package.

The netstat man page lists ss as the superior alternative. The netstat tool is still available to use. However, ss is a better and faster option.

Conclusion

The ss tool allows the investigation of socket and network statistics with advanced filtering options for a better troubleshooting experience. This utility is a must-know tool for any system and network administrator.

Check out our list of the best network security tools to minimize threats to your network environment.

Milica Dancuk
Milica Dancuk is an aspiring technical writer at phoenixNAP and a data nerd. Her background in Electrical Engineering and Computing and her teaching experience give her a unique set of skills - being able to easily explain complex technical concepts through her content.
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