Mortiferr Personally, I wouldn't use cloud 9 as it is you have to keep logging into it to keep your site online, you are better off using it to install Flarum via composer and then transferring the files to either another host with ssh or to a shared hosting platform that supports FTP, php and mysql.
Install composer on cloud 9 (or any other Linux based platform):
curl -sS https://getcomposer.org/installer | php
sudo mv composer.phar /usr/local/bin/composer
After that, create an empty folder, open the terminal in that folder, and from there, follow the Flarum install instruction.
http://flarum.org/docs/installation/
Right click the folder that you installed Flarum in and click download, it will be downloaded as a zip which can be uploaded to your shared hosting via FTP.
If you really want to install it on cloud 9, visit here:
https://community.c9.io/t/setting-up-mysql/1718
Make sure that when you create a new app, select php, when you want to run your installation, there should be a button to start the server, it should say Run.
