How to Check Open Ports

Prerequisites

Before checking open ports, make sure you have:

• SSH access to your VPS
• Root or sudo privileges (for full port listing)

Method 1: Using netstat

Connect to your VPS:

ssh hxroot@YOUR_SERVER_IP -p 22

Install net-tools if needed:

apt install net-tools -y

Show all listening ports:

netstat -tulpn

Output example:

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1234/sshd
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      5678/nginx
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      5678/nginx

Options explained:

• -t - TCP ports
• -u - UDP ports
• -l - Listening ports only
• -p - Show program name/PID
• -n - Numeric (no DNS resolution)

Method 2: Using ss (Modern Replacement)

Show all listening ports:

ss -tulpn

Show TCP listening ports:

ss -tln

Show UDP listening ports:

ss -uln

Method 3: Using lsof

Install lsof:

apt install lsof -y

Show all listening ports:

lsof -i -P -n | grep LISTEN

Check specific port:

lsof -i :80

Method 4: Using nmap (External Scan)

Install nmap:

apt install nmap -y

Scan localhost:

nmap localhost

Scan specific ports:

nmap -p 1-1000 localhost

Method 5: Check Specific Port

netstat -tulpn | grep :80

Check if port is open using nc:

nc -zv localhost 80

Understanding Port States

• LISTEN - Port is open and accepting connections
• ESTABLISHED - Active connection
• CLOSE_WAIT - Connection closing
• TIME_WAIT - Connection closed but waiting