[Discuss] du question

[John Abreau]

du measures disk usage, not individual file size. Two hard links to the
same underlying file in two different directories don't use twice the disk
space of one instance.

If you run two separate instances of du on each of the directories
containing the hard links to that file, each would report 35G. If you run a
single instance of du to measure both, it would report an aggregate total
of 35G; the first one displayed would show as 35G of disk space used and
the second as zero additional disk space used.


On Thu, Jun 8, 2017 at 5:35 PM, dan moylan <jdm at moylan.us> wrote:

>
> dan ritter writes:
> > On Thu, Jun 08, 2017 at 02:11:22PM -0400, dan moylan wrote:
>
> > > dan ritter writes:
>
> > > > > I don't know backintime, but I'm guessing it uses links to
> > > > > do file-level snapshots.   Bet there's a FAQ.
>
> > > > > 35G     20170607-120002-419
> > > > > 86M     20170607-230005-357
>
> > almost as if there were 86MB of changes in between the
> > first and second snapshots.
>
> of course, that's the whole point of backintime.  it
> was/is/has been obvious, even to me, but it is not the
> question and never has been.
>
> my question was and is: why does
>   du -s *
> show 86MG for the second and now third backups, and
>   du -s 20170607-230005-357
> as well as
>   du -hd1 20170607-230005-357
> show 35MB?
>
> this is not obvious to me -- if it is to you, please
> explain.
>
> tia,
> ole dan
>
> j. daniel moylan
> 84 harvard ave
> brookline, ma 02446-6202
> 617-777-0207 (cel)
> jdm at moylan.us
> www.moylan.us
> [no html pls]
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John Abreau / Executive Director, Boston Linux & Unix
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