-If no
-.I userid
-is specified, `root' is assumed.
-To remind the super-user of his responsibilities,
-the Shell substitutes `#' for its usual prompt.
-.SH "SEE ALSO"
-sh(1)
-.SH BUGS
-Local administrative rules cause restrictions to
-be placed on who can
+By default, your environment is unmodified with the exception of
+\fIUSER\fP, \fIHOME\fP, and \fISHELL\fP. \fIHOME\fP and \fISHELL\fP
+are set to the target login's \fI/etc/passwd\fP values. \fIUSER\fP
+is set to the target login, unless the target login has a UID of 0,
+in which case it is unmodified. The invoked shell is the target
+login's. This is the traditional behavior of \fIsu\fP.
+.PP
+The \fI-l\fP option simulates a full login. The environment is discarded
+except for \fIHOME\fP, \fISHELL\fP, \fIPATH\fP, \fITERM\fP, and \fIUSER\fP.
+\fIHOME\fP and \fISHELL\fP are modified as above. \fIUSER\fP is set to
+the target login. \fIPATH\fP is set to ``/usr/ucb:/bin:/usr/bin''.
+\fITERM\fP is imported from your current environment. The invoked shell
+is the target login's, and \fIsu\fP will change directory to the target
+login's home directory.
+.PP
+The \fI-m\fP option causes the environment to remain unmodified, and
+the invoked shell to be your login shell. No directory changes are
+made. As a security precaution, if the
+.I -m
+option is specified, the target user's shell is a non-standard shell
+(as defined by \fIgetusershell\fP(3)) and the caller's real uid is
+non-zero,