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I just encountered this command on a linux forum online where the author warned that donot try this command for curiosity. So my curiosity comes. What is the meaning of command “:() { :|:& }; :” in shell?

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marked as duplicate by RedGrittyBrick, BloodPhilia, terdon linux Aug 8 '14 at 12:44

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

See Fork bomb for that is what it is. – Dan D. Aug 8 '14 at 9:37
up vote 4 down vote accepted

This fork bomb is described here

In bash, a function can be defined

function_name() { ... }

where ... is the implementation or body of the function

:(){ ... }

defines a function named :.


runs the function within itself - that is recursively, and pipes it's output to another invocation of itself.


runs the preceding command in the background.

So that gives us :(){:|:&} to define this function


separates the command defining the function from the following command on the same line (like cd;pwd)


is a final command invocation which starts running the newly defined function.

Normally, I'd hope that per-user limits on processes or other resources would limit the effect of a fork bomb of this sort. Wikipedia has a description of defusing a fork bomb

Addendum: After writing this answer I noticed this question was a duplicate of

Other related questions

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Noted with many thanks! – user3872279 Aug 8 '14 at 10:10
And also related Why is whitespace sometimes needed around metacharacters? with a funny story around :) – fedorqui Aug 8 '14 at 11:24

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