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Date: Wed, 29 Apr 2020 13:42:04 +0200
From: Jirka Vejrazka <>
To: Morgan Woodward <>
Subject: Re: Reduce CPU load. Is it possible?

There is a setting in john.conf that asks JtR to only use CPU cycles that
would otherwise be idle. It's set to "on" by default. So your CPU is at max
usage (that's a good thing for password cracking!) but if any other program
needs the CPU time, JtR will step aside.

Why would you want to throttle to 80% CPU usage? If you are worried about
temperatures or noise, you should probably move the password cracking
job(s) to a different hardware. Most crackers are written in a way that
squeezes as much power from existing hardware as possible to speed up the

Your other option is to limit number of cores on multi-core system - that
would reduce the overall system CPU usage (and slow down cracking).



On Wed, 29 Apr 2020 at 12:42, MA40 <> wrote:

> Hi.
> When John the Ripper is running, the CPU is overloaded (95% in my case).
> Would it be possible to configure it so that it does not work at full
> capacity so as not to load the CPU so much? For example, configure it to
> work at 80%.
> Thank you.
> MA40.

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