Re: dpkg and hardlinks
On Tue, Mar 24, 2009 at 02:34:09PM +0100, Jerome Warnier <jwarnier@beeznest.net> wrote:
> Giacomo A. Catenazzi wrote:
> > Jerome Warnier wrote:
> >> Raphael Hertzog wrote:
> >>> On Tue, 24 Mar 2009, Jerome Warnier wrote:
> >>>
> >>>> For files from packages, though, deduplication might be a good
> >>>> idea, as
> >>>> dpkg is supposedly the only one to ever modify the files (under
> >>>> /usr for
> >>>> example).
> >>>> I don't know however how dpkg treats hardlinks. Does it "break" the
> >>>> hardlink before replacing a file or does it replace the file whatever
> >>>> its real nature is?
> >>>>
> >>> IIRC dpkg preserves hardlinks inside a binary package but I don't
> >>> see how
> >>> it could do the same across multiple binary packages.
> >>>
> >> Oh, I didn't expect it to. I just wanted to know its behaviour when it
> >> upgrades a package.
> >> Before the upgrade, the file is a hardlink (because I hardlinked it
> >> manually), then it tries to upgrade the file/hardlink. Does it "break"
> >> the hardlink* before upgrading the file or does it overwrite the
> >> file/hardlink and all of its "siblings"?
> >
> > Do you really care? (not theoretically, but in normal use).
> > I would expect that same content will be delivered:
> > - by "brother" packages (same source), thus usually updated
> > at the same time.
> > - in documentation (so maybe not so important for your use).
> >
> > I think the most problem are in files outside "dpkg" control,
> > i.e. /var and /etc.
> >
> > I'm just curious: do you have a list of "same" content files?
> > maybe I'm completely wrong.
> Here you are, for /usr on a typical Lenny AMD64 server (generated with
> "finddup -n" from package perforate):
> http://glouglou.beeznest.org/~jwarnier/usr-duplicates.list.gz
$ zcat usr-duplicates.list.gz | awk '{t+=$1*(NF-2)}END{print t}'
33142129
You would free 33MB. How big is your disk ? Is it worth bothering ?
You can get much more free space than that by reducing the number of inodes
supported by your filesystem:
For instance, on my / fs, that contains /usr, and is only 3GB:
Inode count: 384000
Free inodes: 314133
I will obviously never use that many inodes... Now, consider an inode
is 128 bytes (or even 256 in some cases), and do some maths...
Mike
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