1. Before user sign in, the '/etc/rc$runlevel.d/*' will be execute according the runlevel.
2. After user sign in, the Ubuntu9.10 will execute below scripts list below:
a. first, the global '/etc/profile' will be excuted;
b. second, '/etc/profile' will invoke '/etc/profile.d/*.sh';
c. third, '/etc/bash.bashrc' will be executed.
