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Date: Sun, 23 Feb 2014 12:29:14 +0100
From: magnum <>
Subject: Pause/abort from filesystem stimuli

Off-list, on 2014-02-23 10:38, magnum wrote:
> On 2014-02-22 22:14, Solar Designer wrote:
>> Maybe we need to add a feature to JtR where it could be paused by another
>> user on the system (when that feature is enabled in the config) - e.g.,
>> maybe it could check for /var/run/john/pause every few seconds, and we'd
>> add users permitted to use this feature to a group with write access to
>> /var/run/john.  Maybe it should honor the /var/run/john/pause file only
>> as long as its timestamp is recent (so that if someone forgets to remove
>> the pause file, john would eventually resume cracking).
> That might be a good idea. Maybe also /var/run/john/abort to gracefully
> stop a job.

A really KISS patch would check those files right after session-save, 
not introducing any more timers and with ignorable overhead. But that 
could mean a very long reaction time (though normally within 10 minutes).

So maybe the "pause" check should be more frequent (is a configurable 
polling interval overkill?) while the "abort" check could be made at 
session save because it'd need to wait for that anyway.

Also, perhaps both path/file names should be configurable too. This way 
the features could be triggered from any lock/pid file of choice.

If someone creates both files, behavior is yet to define %-)

AbortFile = /var/run/john/abort
PauseFile = /var/run/john/pause
PauseFilePollInterval = 60
MaxPauseFileAge = 7200

We could opt to make abort behave somewhat like ctrl-c - at first 
trigger we set event_abort and if still running after another polling 
interval we abort without saving. Then we'd rename the above 
PauseFilePollInterval to TriggerFilePollInterval.


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