Using a secure system

Using su to access another account

The su(C) command allows you to become another user without logging off. su cannot be used to simply assume the login of another user; instead, su can be used under four circumstances:

The superuser (root) can ``su'' to any account.
A user with the su authorization can ``su'' to root (for example, to become root temporarily after having su'd to a different account).
Users can ``su'' to their own accounts.
A system daemon can ``su'' to an account.
Under ``traditional'' security, any user can ``su'' to any account with that account's password.

To use su, the appropriate password must be supplied (unless you are already root). If the password is correct, su executes a new shell with the real and effective user ID's set to that of the specified user. (If the system is running under tight security, the login user ID is unchanged; otherwise that, too, is changed to the ID of the specified user.)