How to Check Open Ports on Linux: Simple Commands

To check open ports on Linux, use the ss -tuln or netstat -tuln commands to list listening TCP and UDP ports. Alternatively, lsof -i shows open network connections with process details.

Syntax

Here are common commands to check open ports on Linux:

• ss -tuln: Shows listening TCP and UDP ports with numeric addresses.
• netstat -tuln: Lists listening TCP and UDP ports (may require installation).
• lsof -i: Lists open internet sockets with process info.

bash

ss -tuln
netstat -tuln
lsof -i

Example

This example uses ss -tuln to show open ports and their states.

bash

ss -tuln

Output

Netid  State      Recv-Q Send-Q Local Address:Port               Peer Address:Port
udp    UNCONN     0      0      0.0.0.0:68                      0.0.0.0:*
tcp    LISTEN     0      128    0.0.0.0:22                      0.0.0.0:*
tcp    LISTEN     0      128    [::]:22                         [::]:*

Common Pitfalls

Common mistakes when checking open ports include:

• Running netstat without root privileges may show incomplete info.
• Using ss without -n can show hostnames instead of numeric ports, which is slower.
• Not installing net-tools package if netstat is missing.

bash

netstat -tuln
# Wrong: netstat -tul (missing -n shows names, slower)
# Right: netstat -tuln

Quick Reference

Command	Description
ss -tuln	Show listening TCP/UDP ports with numeric addresses
netstat -tuln	List listening TCP/UDP ports (may need net-tools)
lsof -i	List open internet sockets with process info
sudo lsof -i :80	Check which process uses port 80
ss -tunap	Show all TCP/UDP ports with process info (requires root)

Key Takeaways

Use ss -tuln for a fast, modern way to list open ports.

Install net-tools if netstat is not available.

Add -n to avoid slow hostname resolution.

Use lsof -i to see which processes use network ports.

Run commands with sudo for complete information.