httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName
解決辦法非常簡單：
[email protected]:/etc/apache2# vi apache2.conf 
# Include the virtual host configurations:
ServerName  localhost:80
Include sites-enabled/
[email protected]:/etc/apache2# service apache2 restart
 

[ ok ] Restarting web server: apache2 ... waiting ..

遇到問題2：
Apache passenger stopped work after upgrade passenger from 5.1.12 to 5.20
passenger需要安裝老版本的，利用
https://www.redmine.org/issues/28190
解決

I resolve this problem with downgrade passenger version.

1) Uninstall new version:
apt-get remove -y passenger libapache2-mod
 
-passenger

2) Install specific version:
sudo apt-get install passenger=1:5.1.12-1~trusty1
sudo apt-get install libapache2-mod-passenger=1:5.1.12-1~trusty1
sudo apt-get install passenger-dev=1:5.1.12-1~trusty1

3) Enaple apache module:
sudo a2enmod passenger

4) Restart apache:
sudo service apache2 restart
 

遇到問題3：
在配置資料庫的時候，一定要保證使用者名稱和密碼是對的，我就配錯了，導致坑了好久。