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SubjectRe: Is there a "blackhole" /dev/null directory?
Jan Engelhardt wrote:
> On Feb 14 2008 10:46, Andi Kleen wrote:
>> Jasper Bryant-Greene <> writes:
>>> This could be done fairly trivially with FUSE, and IMHO is a good use
>>> for FUSE because since you're just throwing most data away, performance
>>> is not a concern.
> There is a much more interesting 'problem' with a "/dev/null directory".
> Q: Why would you need such a directory?
> A: To temporarily fool a program into believing it wrote something.

Also: to let a program believe it was creating files which are used to
hold the written data. Otherwise /dev/null would probably be the solution.
> Q: Should all files disappear? (e.g. "unlink after open")
> A: Maybe not, programs may stat() the file right afterwards and
> get confused by the "inexistence".

I think what is going to happen is that files created behave as if they
are the result of a mknod resulting in a /dev/null clone.
> Q: What if a program attempts to mkdir /dev/nullmnt/foo to just
> create a file /dev/nullmnt/foo/barfile?
> A: /dev/nullmnt/foo must continue to exist or be accepted for a while,
> or perhaps for eternity.

The directory structure can persist, it's the writing of data which can
be avoided.

Real example:

A program which reads log files and prepares a whole raft of reports in
a directory specified. If you just want to see the summary (stdout) and
exception notices (stderr) having a nulldir would avoid the disk space
and i/o load if you were just looking at the critical output rather than
the analysis.

Yes, if this was an original program requirement it would or should have
been a feature. Real world cases sometimes use tools in creative ways.

Bill Davidsen <>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot

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