[Discuss] du question

[worley at alum.mit.edu (Dale R. Worley)]

dan moylan <jdm at moylan.us> writes:
> looking at the sizes of the directories created by
> backintime i am puzzled by a directory which shows up as
> 86M in one instance and 35G in another.  can someone
> please explain what's going on.

> moylan 1[1631] du -s *
> 35G	20170607-120002-419
> 86M	20170607-230005-357

My first guess is that you have a version of du that attempts to not
count a file twice if there are two links to it.  Since the two
directory names ultimately link to many of the same files, the second of
them will have an artificially low disk usage total.

The way to check this is to run du on these directories in different
ways.  This method will be free of the effect that I suspect:

    $ du -s 20170607-120002-419
    $ du -s 20170607-230005-357

Do they produce similar values?  Or consider

    $ du -s 20170607-230005-357 20170607-120002-419

In this case, 20170607-120002-419 appears *second* and should have a
total much smaller than the total reported in your example.

Dale