su [OPTION]... [-] [USER [ARG]...]


       Change the effective user id and group id to that of USER.

       -, -l, --login
              make the shell a login shell

       -c, --commmand=COMMAND
              pass a single COMMAND to the shell with -c

       -f, --fast
              pass -f to the shell (for csh or tcsh)

       -m, --preserve-environment
              do not reset environment variables

       -p     same as -m

       -s, --shell=SHELL
              run SHELL if /etc/shells allows it

       --help display this help and exit

              output version information and exit

       A mere - implies -l.   If USER not given, assume root.