1. http://www.unixmen.com/install-vsftp-with-virtual-users-on-centos-rhel-scientific-linux-6-4/
2. http://centosforserver.blogspot.tw/2010/02/virtual-hosting-with-vsftpd-and-mysql.html
3. http://blog.imomo.tw/blog/2013/04/19/vsftpd-virtual-user-shi-zuo-bi-ji/
4. http://infofreund.de/user_quotas_vsftpd_en/
