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Re: Recursively calling a bash script goes undetected and eats all syste


From: Diggory Hardy
Subject: Re: Recursively calling a bash script goes undetected and eats all system memory
Date: Fri, 10 Dec 2010 10:25:02 +0100
User-agent: KMail/1.13.5 (Linux/2.6.32-5-amd64; KDE/4.5.3; x86_64; ; )

On Thursday 09 December 2010 Pierre Gaston wrote:
> On Wed, Dec 8, 2010 at 11:15 AM, Diggory Hardy <address@hidden> wrote:
> > Hello,
> >
> > With a simple script such as that below, bash can enter an infinite loop of 
> > eating memory until the system is rendered unusable:
> >
> > #!/bin/bash
> > PATH=~
> > infinitely-recurse
> >
> > Save this as infinitely-recurse in your home directory and run - and make 
> > sure you kill it pretty quick. OK, so an obvious bug when put like this, 
> > though it bit me recently (mistakenly using PATH as an ordinary variable 
> > and having a script with the same name as a system program). Would it not 
> > be simple to add some kind of protection against this — say don't let a 
> > script call itself more than 100 times?
> >
> > Thanks,
> > Diggory
> >
> Well, I'm not a big fan of the technique, but out there I see a lot of
> wrapper scripts calling themselves to automatically restart an
> application.
> 
Uh. Then over time it is legitimate to have a script recursively call itself a 
few thousand times with each instance still in memory?

The potential to grind the system to a complete halt is pretty serious though. 
Perhaps the ideal solution would be to have the kernel intervene before it 
starts thrashing memory, but that doesn't seem to happen.



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