> > Linux does not have security levels. The a and i bits can, however, be reset
> > only by the superuser; this may or may not be comparable to the fact that the
> > "security level" can only be reset by the superuser in 4.4bsd.
> It is my understanding that the only way to lower the security level is
> to reboot the system.
Linus HAS security level. It is 'increase only' by writing to
/proc/sys/kernel/securelevel. In secure level 1 immutable and append only
flags can't be removed. Of course using hardware write protected media is
even more secure.