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Date: Fri, 4 Nov 2016 15:14:31 +0100
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: John does not fork as many times as I want

On Fri, Nov 04, 2016 at 02:59:10PM +0100, matlink wrote:
> I've omitted to tell something:
> 
> after these missing forks, the main process returns me:
> 
> 1:Fork: cannot allocate memory
> 
> which explains why all forks are not poped.

Oh, sure.  Sounds like you're cracking the full(er) LinkedIn dump than
was circulating in 2012, then, and your use of the "-linkedin" format is
inappropriate.  Please use the simple "raw-SHA1" format instead.  And
please use bleeding-jumbo.

> However it seems that I
> still have plenty of available memory (about 200GB free).

You say you're requesting 40 forks, but only 5 processes are left.
This may mean that some of the other 35 were forked, fought for memory,
and then died - freeing up that 200 GB that you see.

> Can this error come from another situation than lack of memory?

There are many other possibilities, but they are not likely in your case.

The way "--fork" works, it does not multiply the memory needs of one
process by the number of processes right away.  Most of the memory pages
are shared between the processes.  However, when a lot of passwords get
cracked, the differences between the processes increase, and fewer pages
are shared.  Thus, when cracking large password hash dumps like this,
you need to start with fewer forked processes to get the easiest
passwords cracked first, then after a few hours or days, when there are
relatively few hashes left to crack (e.g., 20% of original) and the
successful guesses are not as frequent, restart with your desired number
of processes.

There were some changes in bleeding-jumbo (since 1.8.0-jumbo-1) that
should partially mitigate this issue, so maybe you'd be able to run more
processes with it now, but overall my suggested approach above is still
the way to go.

Alexander

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