In RedHat 6.1 and 6.2, if you log in from a vty and call from the shell
login by exec login, it begins to fill the screen "login:"s and not
listening on it
any more. Perhaps this causes the problem if I try to log in to my Linux
via modem by mgetty.
login is no longer setuid root, therefore, 'exec login' won't
work any more.