\fBsu\fR is used to become another user during a login session\&. Invoked without a username, \fBsu\fR defaults to becoming the super user\&. The optional argument \fB\-\fR may be used to provide an environment similar to what the user would expect had the user logged in directly\&.
Additional arguments may be provided after the username, in which case they are supplied to the user<65>s login shell\&. In particular, an argument of \fB\-c\fR will cause the next argument to be treated as a command by most command interpreters\&. The command will be executed by the shell specified in \fI/etc/passwd\fR for the target user\&.
The user will be prompted for a password, if appropriate\&. Invalid passwords will produce an error message\&. All attempts, both valid and invalid, are logged to detect abuses of the system\&.
The current environment is passed to the new shell\&. The value of \fI$PATH\fR is reset to \fI/bin:/usr/bin\fR for normal users, or \fI/sbin:/bin:/usr/sbin:/usr/bin\fR for the super user\&. This may be changed with the \fIENV_PATH\fR and \fIENV_SUPATH\fR definitions in \fI/etc/login\&.defs\fR\&.
A subsystem login is indicated by the presence of a "*" as the first character of the login shell\&. The given home directory will be used as the root of a new file system which the user is actually logged into\&.
