Check Port Used in Linux

Linux provides several tools that allow you to quickly see which ports are in use and which applications are using those ports.

netstat

netstat is a classic utility that can display network connections, routing tables, and protocol statistics.

sudo netstat -tuln

Explanation:

• -t: Show TCP connections

• -u: Show UDP connections

• -l: Show only listening sockets (active ports)

• -n: Display addresses in numeric format (skip DNS resolution)

ss

ss is a more modern and faster tool than netstat for analyzing socket connections. ss displays similar information to netstat but with better performance.

sudo ss -tuln

lsof

lsof (list open files) can show detailed information on network ports and the specific processes using them.

sudo lsof -i -P -n

You can specify a specific port to search for processes.

lsof -i :<port_number>

Explanation:

• -i: Show all network files

• -P: Use port numbers instead of names

• -n: Skip DNS lookup for faster results

nmap

If you want to check open ports on your system from an external perspective, nmap (network mapper) is a useful tool.

sudo nmap -sT -O localhost

Explanation:

• -sT: TCP connect scan

• -O: Detect the operating system