nginx: bind() failed (98: Address already in use)

What the message looks like

nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

Common causes

• Apache, another nginx instance or a panel service (Plesk, cPanel) already listens on port 80 or 443.
• nginx is already running and was started a second time instead of reloaded.
• A Docker container publishes the same port, e.g. -p 80:80.
• A stale nginx master process survived a crash or a bad restart.
• Two services were set to the same listen address and port in your own configuration.

Check

1. Who listens on port 80 and 443?
   ss -ltnp | grep -E ':(80|443) 'Copy
2. Is the configuration valid? (a port conflict only shows up on start)
   nginx -tCopy
3. Look for leftover nginx processes
   ps aux | grep '[n]ginx'Copy
4. Containers that publish ports
   docker ps --format '{{.Names}} {{.Ports}}'Copy

Fix

• Stop and disable the other service if it should not run: systemctl disable --now apache2.
• If nginx itself is running, use systemctl reload nginx instead of starting it again.
• Kill only a clearly stale master process, then start the service: pkill nginx; systemctl start nginx.
• Move one of the services to another port, or bind each to its own IP address: listen 203.0.113.10:80;.
• On a server with a panel, change the setting in the panel and do not start a second nginx by hand.

FAQ

nginx -t says OK but nginx still does not start. Why?

nginx -t checks the syntax and files, but it does not occupy the ports. A port conflict only appears when nginx really starts, so always read the output of ss -ltnp too.

Can two services share port 80?

Only if they listen on different IP addresses. For the same address and port, one of them has to move or sit behind the other as a reverse proxy.