How To Fix Nginx "Address Already In Use" Error?

Check for Processes Using the Port

To find which process is using the port Nginx wants to use, use the netstat command. This command shows active network connections and their processes.

Run this command in your terminal:

sudo netstat -tulpn

This command will show a list of all active connections. Look for entries with the port number Nginx is trying to use (usually 80 or 443). The output will show the process ID (PID) and name of the program using that port.

sudo kill [PID]

Verify Nginx Configuration

After checking for conflicting processes, review your Nginx configuration files for errors or misconfigurations.

To check for syntax errors in your Nginx configuration files, use this command:

sudo nginx -t

This command will test your configuration files and report any syntax errors.

Next, check your Nginx configuration files to make sure the port settings are correct. Look for the 'listen' directive in your server blocks. Make sure it matches the port you want Nginx to use. For example:

server {
    listen 80;
    # Other configuration settings
}

If you're using HTTPS, you might also have a server block listening on port 443:

server {
    listen 443 ssl;
    # SSL certificate settings and other configurations
}

By checking these areas, you can find the source of the "Address Already In Use" error and take steps to fix it.

Terminating Conflicting Processes

To fix the "Address Already In Use" error, stop processes using the required port. Use the kill command:

sudo kill -2 [PID]

Replace [PID] with the process ID found using the netstat command. The -2 option sends a termination signal.

Another method is the fuser command:

sudo fuser -k 443/tcp

This command stops all processes using port 443 over TCP.

sudo lsof -i :80

Modifying Nginx Configuration

If the error continues, adjust your Nginx configuration. Use the correct syntax for IPv4 and IPv6 listening:

For IPv4 only:

server {
    listen 80;
}

For both IPv4 and IPv6:

server {
    listen 80;
    listen [::]:80;
}

For IPv6 only:

server {
    listen [::]:80 ipv6only=on;
}

Restarting Nginx Service

After changes, restart Nginx:

sudo systemctl restart nginx

Or on systems using the service command:

sudo service nginx restart

To check if Nginx restarted, view its status:

sudo systemctl status nginx

This command shows if Nginx is active and running without errors. If you still see the "Address Already In Use" error, review your configuration and check if other processes are using the required ports.