v7 man page for su

SU(1)							      General Commands Manual							     SU(1)

NAME
       su  -  substitute user id temporarily

SYNOPSIS
       su [ userid ]

DESCRIPTION
       Su  demands  the  password of the specified userid, and if it is given, changes to that userid and invokes the Shell sh(1) without changing
       the current directory or the user environment (see environ(5)).	The new user ID stays in force until the Shell exits.

       If no userid is specified, `root' is assumed.  To remind the super-user of his responsibilities, the Shell substitutes `#'  for	its  usual
       prompt.

SEE ALSO
       sh(1)

																	     SU(1)