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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