The Immutable File Attribute

As you probably know, the chattr and lsattr commands set and view file =
attributes in Linux and other UNIX OSes. The immutable flag is =
interesting because it prevents even root from modifying the file when =
it is set. However, root can casually set or remove the flag any time =
so it does not stand as a difficult barrier. =20

I understand that in HP-UX you have to be in single-user mode to change =
this attribute. Is there a way to make Linux act in the same manner? =
This would be a nice security restriction if critical files could not be =
modified except by root in single-user mode. Does anyone know a way to =
do this?

Thanks,

Brian