Re: Resource limits

[Al Boldi <a1426z@gawab.com>]

Neil Horman wrote:
> On Tue, Sep 27, 2005 at 04:42:07PM +0300, Al Boldi wrote:
> > Neil Horman wrote:
> > > On Tue, Sep 27, 2005 at 08:08:21AM +0300, Al Boldi wrote:
> > > > Neil Horman wrote:
> > > > > On Mon, Sep 26, 2005 at 11:26:10PM +0300, Al Boldi wrote:
> > > > > > Neil Horman wrote:
> > > > > > > On Mon, Sep 26, 2005 at 08:32:14PM +0300, Al Boldi wrote:
> > > > > > > > Neil Horman wrote:
> > > > > > > > > On Mon, Sep 26, 2005 at 05:18:17PM +0300, Al Boldi wrote:
> > > > > > > > > > Rik van Riel wrote:
> > > > > > > > > > > On Sun, 25 Sep 2005, Al Boldi wrote:
> > > > > > > > > > > > Too many process forks and your system may crash.
> > > > > > > > > > > > This can be capped with threads-max, but may lead
> > > > > > > > > > > > you into a lock-out.
> > > > > > > > > > > >
> > > > > > > > > > > > What is needed is a soft, hard, and a special
> > > > > > > > > > > > emergency limit that would allow you to use the
> > > > > > > > > > > > resource for a limited time to circumvent a
> > > > > > > > > > > > lock-out.
> > > > > > > > > > >
> > > > > > > > > > > How would you reclaim the resource after that limited
> > > > > > > > > > > time is over ?  Kill processes?
> > > > > > > > > >
> > > > > > > > > > That's one way,  but really, the issue needs some deep
> > > > > > > > > > thought. Leaving Linux exposed to a lock-out is rather
> > > > > > > > > > frightening.
> > > > > > > > >
> > > > > > > > > What exactly is it that you're worried about here?
> > > > > > > >
> > > > > > > > Think about a DoS attack.
> > > > > > >
> > > > > > > Be more specific.  Are you talking about a fork bomb, a ICMP
> > > > > > > flood, what?
> > > >
> > > > Consider this dilemma:
> > > > Runaway proc/s hit the limit.
> > > > Try to kill some and you are denied due to the resource limit.
> > > > Use some previously running app like top, hope it hasn't been killed
> > > > by some OOM situation, try killing some procs and another one takes
> > > > it's place because of the runaway situation.
> > > > Raise the limit, and it gets filled by the runaways.
> > > > You are pretty much stuck.
> > >
> > > Not really, this is the sort of thing ulimit is meant for.  To keep
> > > processes from any one user from running away.  It lets you limit the
> > > damage it can do, until such time as you can control it and fix the
> > > runaway application.
> >
> > threads-max = 1024
> > ulimit = 100 forks
> > 11 runaway procs hitting the threads-max limit
>
> This is incorrect.  If you ulimit a user to 100 forks, and 11 processes
> running with that uid

Different uid.

> If you have a user process that for some reason legitimately needs to try
> use every process resource available in the system, then yes, you are prone
> to a lock out condition

Couldn't this be easily fixed in kernel-space?

Thanks!

--
Al