how : ( ) { : | : & } ; : works

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How does this bash fork bomb work?

Hi,

quick questions.

How does this shell command works and why it gains the cpu usage up to 100% ?

: ( ) { : | : & } ; :

Granted, this is pretty hard to google ;-) (unless you know it's called a "fork bomb"). — Joachim Sauer, Apr 20 '11 at 13:54

score 6 · Answer 1 · answered Apr 20 '11 at 14:00

Here is the short explanation coursey of wikipedia (http://en.wikipedia.org/wiki/Fork_bomb):

:()      # define ':' -- whenever we say ':', do this:
{        # beginning of what to do when we say ':'
    :    # load another copy of the ':' function into memory...
    |    # ...and pipe its output to...
    :    # ...another copy of ':' function, which has to be loaded into memory
         # (therefore, ':|:' simply gets two copies of ':' loaded whenever ':' is called)
    &    # disown the functions -- if the first ':' is killed,
         #     all of the functions that it has started should NOT be auto-killed
}        # end of what to do when we say ':'
;        # Having defined ':', we should now...
:        # ...call ':', initiating a chain-reaction: each ':' will start two more.

Basically a recursive function, with each recusrive call resulting in two more processes. So the number of processes grows exponentially.

score 2 · Accepted Answer · answered Apr 20 '11 at 13:54

2

This is a Fork Bomb

answered Apr 20 '11 at 13:54

Roman Cheplyaka

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how : ( ) { : | : & } ; : works

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