sudo bash : change the current user into root
su u1: change the current user into u1
useradd: add new user into system
userdel: delete a user from system
groups: check a user‘s group information
chown: chang a file‘s owner
chmod: chang a file‘s mod
gpasswd -a u3 foo: add user into a group
su u1 -c "./objput doc<testfile"
原文：http://www.cnblogs.com/airwindow/p/4055330.html