netstat (Network Statistics)
The netstat command generates displays that show network status and protocol statistics. It is an invaluable tool for finding out which ports are open on your machine and which services are using them.
1. Basic Usage
netstat [options]
2. Key Options (Common Combo: -tulpn)
| Option | Name | Description |
|---|---|---|
-a |
All | Displays all active connections and listening ports. |
-n |
Numeric | Shows IP addresses and port numbers as numbers. |
-t / -u |
TCP/UDP | Filters by TCP or UDP protocols. |
-l |
Listening | Shows only the sockets currently listening for incoming connections. |
-p |
Programs | Shows the PID and name of the program to which each socket belongs. |
3. Practical Examples
① List all listening TCP and UDP ports with PID
sudo netstat -tulpn
② Checking routing information
netstat -rn
③ Continuous monitoring
Update the statistics every 5 seconds.
netstat -c 5
4. [Tip] The modern alternative: ss
On newer Linux systems, netstat is being replaced by the ss command (Socket Statistics). ss is faster and provides more detailed information.
ss -ant