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Subject: Fork bomb question about Cygwin
Thread-Topic: Fork bomb question about Cygwin
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Date: Wed, 21 Jan 2026 20:37:52 +0000
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From: "Lavrentiev, Anton \(NIH/NLM/NCBI\) \[C\] via Cygwin" <cygwin AT cygwin DOT com>
Reply-To: "Lavrentiev, Anton \(NIH/NLM/NCBI\) \[C\]" <lavr AT ncbi DOT nlm DOT nih DOT gov>
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Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

Hello All,

I apologize in advance if my question is off-topic for this mailing list, and if so, y'all are free to just ignore it.

In essence, I was under a (seemingly wrong) impression that user-level classic fork-bomb such as the infamous,

":(){ :|:& };:"

would not be possible because Windows would run out of memory creating the processes, and at some point Cygwin's fork() would fail, thus, stopping the chain reaction.

That obviously is not the case, and the above (run by a non-privileged user) kills the OS quite successfully, rendering it totally non-responsive (even mouse stops moving at some point as well) with only a hardware reset being able to bring it back to life.

(To confirm, I experimented with that on the all current Windows 10 Pro.)

So the first part of my question is, whether this is actually expected to happen?

By default Cygwin creates the user environment with unlimited processes (and I suppose that any user can just run "bash" unrestricted, thus obtaining the unlimited process resource).  Which then brings up a question about security of the system, as a whole.  And so the second part is, is there any way to securely control / restrict the behavior?

Thank you,

Anton Lavrentiev
Contractor NIH/NLM/NCBI


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