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From: ragnar_at_this.is
Date: Wed 18 Jun 2003 - 06:11:17 BST


Quoting Herbert Poetzl <herbert_at_13thfloor.at>:

Ading to Herberts comments.

> On Tue, Jun 17, 2003 at 01:44:00PM -0500, John Goerzen wrote:

> > it can do "copy on write" hard links for binaries
> > between one system and the next.

Yes, but it does not work that way....

tar has a -U option
unlink & recreate files instead of overwriting

Package istallation from .rpm or .deb does this
or rename and copy.

> anyway, there is something called IMMUTABLE-LINK-INVERSION

>From - vserver 0.6 changes log
it looks like this is now part of the ctx patch
but probably only for ext2

Does anyone maintain the modified e2fsprogs package?
Sam's patch is for version 1.25.

> > I have never used this feature since I'm running Debian.
> > However, I'm interested in the mechanics, and I'm wondering
> > if the system can ... "combine" systems post-install.

I know of no problem doing this any time you like.

> it can be used, although it's not copy on write, as you
> will know now ...

copy on write would be better, then one could blindly unify
all files that are the same. If you can work that out, e.g.
using VFS or something you would make many people happy.

Interesting comment from
  GCFS: a Garbage-Collected Filesystem for Linux
This “copy on write” idea is also completely independent
from the GCFS. I should be asking myself whether it could
be implemented in a traditional (gc-less) filesystem, but
every time I try to think about this question,
my mind seems to go bezerk.

> > If I knew the APIs, I'd be happy to write such a tool myself.

You can look at:
fdupes - install with dselect

or a perl script fast-dupemerge

> there where several proposals, and as far as I remember
> Sam is actually maintaining (at least from time to time)
> a tool to unify on debian and similar systems ...

I found unify-dirs at

Also interesting to look at User-mode Linux

-- Sharing Filesystems between Virtual Machines http://user-mode-linux.sourceforge.net/shared_fs.html

-- Host file access http://user-mode-linux.sourceforge.net/hostfs.html

best ragnar

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