link source: https://wiki.archlinux.org/index.php/environment_variables
Setting variables:
Globally:
edit /etc/profile, /etc/bash.bashrc, /etc/environment.
Per User:
~/.bashrc, ~/.profile, ~/.bash_login, ~/.bash_logoutlinux environment variables summary.
原文：http://www.cnblogs.com/huang-kun/p/3987671.html
