Become another user.
su [options] [username]
-c command passes the command to the shell.
-f prevents reading the startup file (.cshrc) when the shell is csh or tcsh.
-l makes the new shell a login shell by reading the user’s startup file.
-p preserves the environment variables HOME, USER, LOGNAME, and SHELL.
-s shell runs the specified shell instead of the user’s default shell.
The su command lets you assume the identity of another user. You have to provide the password of that user before you can continue. If you do not provide a user name, su assumes you want to change to the root user.