How to Check Which Process Is Using a Port in Linux (ss, lsof, netstat)
Problem Overview
When a service fails to start or a port shows as “already in use”, it usually means another process is already listening on that port.
To fix the issue, you first need to identify which process is using the port and stop or reconfigure it safely.
Prerequisites
Before starting, make sure the following conditions are met:
Terminal access with sudo privileges
Basic understanding of services and processes
Solution
- Check port usage with ss (socket statistics), It is the preferred tool on modern Linux systems and replaces
netstat.[root@pythonlinuxhub ~]# sudo ss -tulpn | grep :80 tcp LISTEN 0 511 *:80 *:* users:(("httpd",pid=2899,fd=4),("httpd",pid=2898,fd=4),("httpd",pid=2897,fd=4),("httpd",pid=2892,fd=4))
- Check using
lsof, It lists open files, and in Linux, ports are treated as files.[root@pythonlinuxhub ~]# sudo lsof -i :80 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME httpd 2892 root 4u IPv6 33917 0t0 TCP *:http (LISTEN) httpd 2897 apache 4u IPv6 33917 0t0 TCP *:http (LISTEN) httpd 2898 apache 4u IPv6 33917 0t0 TCP *:http (LISTEN) httpd 2899 apache 4u IPv6 33917 0t0 TCP *:http (LISTEN)This method is very useful when you need user ownership and detailed process info.
- Check using
netstat, It is deprecated but still available on older Linux distributions.[root@pythonlinuxhub ~]# netstat -tulpn | grep :80 tcp6 0 0 :::80 :::* LISTEN 2892/httpdIf
netstatis not installed, install it usingyum install net-tools
Once you identify the PID, inspect it before stopping
ps -fp
- Gracefully stop the process
sudo kill
- If the process does not stop
sudo kill -9
Some ports are opened by services controlled by
systemctl.- Identify the service
sudo systemctl status
- Stop the service safely
sudo systemctl stop
- Prevent if from starting on boot
sudo systemctl disable
- Identify the service
Note:
- Do not kill system-critical services blindly. Always verify what the process is and whether it’s managed by
systemd.
Shaik Mohammed Faruk
Software Engineer sharing practical tutorials and insights on Linux, Python, SQL, and modern technologies.
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