If no username is specified, ``root'' is assumed. You may su to ``root'' only if you are a member of the ``wheel'' group, even if no root password is set. To su to ``root'', you must supply the root password. To remind the super-user of his responsibilities, the Shell substitutes `#' for its usual prompt.
args arguments are passed to the shell of username which su invokes. This allows su to execute commands as another user.
The -f option prevents csh(1) from executing the .cshrc file; thus making su start up faster.
The - option simulates a full login.
An alternative implementation of su is in /bin/su.wheel. This version, which is shipped without the setuid-root bit turned on, allows users in the ``wheel'' group (group 0) to su to ``root'' using either their own password or the root password. This version offers more convenience, but if your site is concerned about the increased potential for security problems, you should continue to use the standard version of su.