See: https://github.com/ONLYOFFICE/DocumentServer/issues/888

Thank you CSchmidtDD Christof T. https://github.com/CSchmidtDD

InstallConfig's Note: ds:example service is NOT disabled by default, at least not in my installation on Ubuntu using the community-edition, and, apparently it is also NOT disabled when using the enterprise-edition installation guide.

CSchmidtDD's Comments: And even if it were disabled, it messes up with the nginx config by having the link to the ds-example.conf in there. The welcome page is messed up by default that way and should not be showing an “example” index.html, at least not for an “enterprise-edition.”

If you installed the Document Server (any edition) and have the same problem - that being, the welcome page was the example index.html, then open a terminal or ssh remotely into your ubuntu or debian server and take the following steps offered by CSchmittDD to get rid of the example:

rm -rf /etc/onlyoffice/documentserver-example/  #Removes the whole unnessecary "example"
rm /etc/nginx/includes/ds-example.conf   #This will delete the link that stops nginx from starting with error like you mentioned
service nginx restart   #Should restart without problem
service supervisord restart  #As Example-Service is gone, it will re-register to only four active packets 
supervisorctl restart docservice   #Restart docservice and now you can see the green checkmark

After these steps, the OnlyOffice-Server should now show you a green checkmark on the welcome page that everything is running correctly.

Hope this fixes your problem(s).

It said there was something missing.

sudo rm -rf /etc/onlyoffice/documentserver-example/  #Removes the whole unessecary "example"
sudo rm /etc/nginx/includes/ds-example.conf   #This will delete the link that stops Nginx from starting with error
sudo service nginx restart   #Should restart without problem