linux-kernel - Re: [Fastboot] Stupid kexec/kdump question...

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20060927052737.GA17214@verge.net.au>
Date:	Wed, 27 Sep 2006 14:27:38 +0900
From:	Horms <horms@...ge.net.au>
To:	Andrew Morton <akpm@...l.org>
Cc:	Valdis.Kletnieks@...edu, fastboot@...ts.osdl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] Stupid kexec/kdump question...

On Tue, Sep 26, 2006 at 10:10:29PM -0700, Andrew Morton wrote:
> On Tue, 26 Sep 2006 11:25:06 -0400
> Valdis.Kletnieks@...edu wrote:
> 
> > OK, I'm running a Fedora Core 6 (rawhide actually) box with -18-mm1 kernel.
> > I've installed kexec-tools and similar, and am trying to get the kernels
> > built following the hints in Documentation/kdump/kdump.txt, but a few
> > questions arise:
> > 
> > 1) Other than the fact that the Fedora userspace looks for a
> > ${kernelvers}kdump kernel, is there any reason the kdump kernel has
> > to match the running one, or can an older kernel be used?

The post-crash kernel is not realy dependant on the pre-crash kernel.
What is important is that either the kernel is relocatable
(which is being worked on for x86 and i386), or it is compiled to
run at a non-default address and that address corresponds
to the region reserved by the crashkernel command line parameter
passed to the pre-crash kernel.

The post-crash kernel will also need CONFIG_CRASH_DUMP 
and likely CONFIG_PROC_VMCORE

> > 2) I'm presuming that a massively stripped down kernel (no sound support,
> > no netfilter, no etc) that just has what's needed to mount the dump location
> > is sufficient?

Yes

> > 3) The docs recommend 'crashkernel=64M@...', but that's 8% of my memory.
> > What will happen if I try '16M@...' instead?  Just slower copying due to
> > a smaller buffer cache space, or something more evil?

There is a lower bound to how small you can make the space, which
is basically how little memory space your post-crash kernel needs.
16M is probably pushing it, but 32M should be more than possible.
Experimentation is really the order of the day here.

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/