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Date: Tue, 24 Jul 2012 13:42:40 +0200
From: magnum <john.magnum@...hmail.com>
To: john-users@...ts.openwall.com
Subject: Re: Confusing --mem-file-size=SIZE description
On 2012-07-24 12:06, Frank Dittrich wrote:
> The parameter --mem-file-size is mentioned in the usage output:
> --mem-file-size=SIZE size threshold for wordlist preload (default 5 MB)
>
> It is also mentioned in doc/OPTIONS.
> --mem-file-size=SIZE max. size of wordlist to preload into memory.
>
> The unit is not mentioned in the description, so I assume it is in bytes.
> That means, to change the value from default 5 MB to 100 MB, I would
> have to use --mem-file-size=100000000. Is that correct?
> It would be nice to clarify this in doc/OPTIONS.
Right.
> The parameter --mem-file-size is also mentioned in doc/README.mpi.
> Here, the special SIZE values 0, 1, 2 are mentioned.
> Apparently, for MPI this parameter is mis-used for something completely
> different. Especially the --mem-file-size=0 meaning in MPI mode is
> unfortunate, since without MPI, this means: load the complete file into
> memory. If you have enough memory, this is usually what you want.
--mem=0 is not different - it's actually where the non-MPI behavior
stems from. MPI or not, it is a short-cut for saying "buffer the file,
no matter its size".
> But for MPI that means, the sequence of password candidates tried will
> not be optimal for wordlists with candidates sorted by popularity.
I guess you base that statement on the incorrect assumption that MPI
will buffer the first 1/n of the wordlist to the first node. This is not
the case. Each node will buffer every n:th word.
> Is this documentation still correct?
>
> If yes, should a new (possibly hidden) parameter replace this obscure
> meaning of --mem-file-size?
> This parameter could be disabled for non-MPI builds.
The --mem=1 or 2 are mostly for debugging so I never gave them real options.
magnum
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