Nginx bind() to 0.0.0.0:80 failed (98: Address already in use)

What the error looks like

Nginx refuses to start, and nginx -t or the service log shows:

nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] still could not bind()

Why it happens

Nginx tries to listen on port 80, but something already holds it. Two common cases:

• Another service owns port 80. Very often it is Apache, installed by default on many boxes and started automatically. Only one program can listen on a port at a time.
• Two nginx blocks both claim it. Two server blocks both marked listen 80 default_server, so nginx conflicts with itself.

How to fix it

1. Find what is holding port 80:

sudo ss -ltnp | grep :80

The output names the process, for example users:(("apache2",pid=812,...)).

2. If it is another service like Apache, stop and disable it so it does not come back on reboot:

sudo systemctl stop apache2
sudo systemctl disable apache2

3. If it is a leftover nginx process, stop it fully before starting again:

sudo systemctl stop nginx
sudo systemctl start nginx

4. If the conflict is a duplicate default_server, only one block per port may have it. Fix the extra one. See testing config safely before you reload:

server {
    listen 80 default_server;
    server_name _;
}

server {
    listen 80;
    server_name example.com;
}

5. Test and start:

sudo nginx -t && sudo systemctl restart nginx

Common mistake

Running nginx by hand while the service is already running. The systemd nginx already holds port 80, and your manual copy cannot bind it. Manage nginx through systemctl, not by launching a second copy.

A small detail that sends people in circles: ss -ltnp only prints the owning process when you run it as root. Without sudo, you see the port is taken but the process column is blank, so it looks like nothing holds it. Always run the check with sudo, or you are diagnosing half-blind.

FAQ

How do I know it is Apache and not nginx?

sudo ss -ltnp | grep :80 prints the process name. If it says apache2 or httpd, Apache has the port. If it says nginx, an nginx process is already running.

What does default_server mean here?

default_server marks the block that handles requests not matched by any server_name on that port. Only one block per port may be the default. Two of them cause this same emerg error.

Same error but on port 443?

Same cause, different port. Something already listens on 443. Run sudo ss -ltnp | grep :443 and stop the conflicting service or remove the duplicate listen 443 default.