Re: IMMUTABLE and APPEND-ONLY rationales

[Jamie Lokier]

Andi Kleen wrote:
> > > Even root cannot delete immutable and append-only files again. So
> > > if every user was allowed to do that he/she could create a lot of
> > > problems for root (like creating undeletable files in /tmp)
> > 
> > Root is already privileged to set/unset those bits on any file regardless
> > of ownership.  It does not follow that this would change if users could
> > set those bits on their own files.  
> 
> In the original implementation (pre 2.0) that wasn't the case when secure
> level was > 0. securelevel was dropped later because it was broken. 
> The root restriction is a leftover.

Given that, it might be useful to enable IMMUTABLE for ordinary user
files.

Here's a use:

  cp -al kernel kernel-branch
  chattr -R +i kernel

Proceed to edit files in `kernel-branch'-- safely knowing that nothing
you do there will alter the files in `kernel'.  (Otherwise commands like
`prog > file' and some editors will change the hard-linked files).

enjoy,
-- Jamie