This is the error I’m getting. I can confirm before installing certbot nginx was working fine (out-of-the-box).
$ sudo systemctl status nginx
nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Mon 2018-02-12 20:52:53 CET; 7min ago
Process: 4805 ExecStart=/usr/sbin/nginx -g daemon on; master_process on; (code=exited, status=1/FAILURE)
Process: 4800 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=0/SUCCESS)
Main PID: 1904 (code=exited, status=0/SUCCESS)
nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)
nginx: [emerg] still could not bind()
systemd[1]: nginx.service: Control process exited, code=exited status=1
systemd[1]: Failed to start A high performance web server and a reverse proxy server.
systemd[1]: nginx.service: Unit entered failed state.
systemd[1]: nginx.service: Failed with result ‘exit-code’.