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Date: Thu, 30 Apr 2020 21:03:50 +0200
From: Solar Designer <>
Subject: Re: Reduce CPU load. Is it possible?

On Thu, Apr 30, 2020 at 07:16:49PM +0200, MA40 wrote:
> Now, he also has John the Ripper running trying to decrypt some Bitcoin
> hashes.

For those, ideally you'd use GPUs.  More importantly though, you'd focus
the attack based on what you recall about the password(s).

> Of course I am interested in maximum power, but I do not want to reduce the
> life of the processor, it is working without too many expectations of
> obtaining any result with John the Ripper.
> That is why I wanted to offload the CPU work a bit. (80% would be fine).

You may use OMP_NUM_THREADS like I described to make JtR use a subset of
your CPU's cores, thereby reducing its heat dissipation.

Darren's suggestion to use "cpulimit" would likely result in efficiency
loss as it'd mess with OpenMP thread synchronization.

I think you never mentioned what OS you're running JtR on.


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