[Soekris] Test the watchdog
mike at jellydonut.org
Wed Jan 14 23:08:14 UTC 2009
On Wed, Jan 14, 2009 at 3:38 PM, Thorsten Mühlfelder <thenktor at gmx.de>wrote:
> So I need a damon, too? I thought it's a kernel only thing because there is
> extra hardware for this task.
> dmesg gives me:
> sc520_wdt: WDT driver for SC520 initialised. timeout=30 sec (nowayout=0)
> On Wed, 14 Jan 2009 15:29:40 -0500
> "Michael Proto" <mike at jellydonut.org> wrote:
> > On Wed, Jan 14, 2009 at 3:10 PM, Thorsten Mühlfelder <thenktor at gmx.de
> > > Hi
> > > As far as I know the net4501 watchdog should reboot the machine when
> > > kernel hangs. How can I test this with Linux?
> > > _______________________________________________
> > > Soekris-tech mailing list
> > > Soekris-tech at lists.soekris.com
> > > http://lists.soekris.com/mailman/listinfo/soekris-tech
> > >
> > I can't speak for the linux version as I run FreeBSD on my ALIX and
> > boards, but I can kill -9 my watchdogd process and the box will reboot
> > within about 15 seconds. I suspect a similar test could be performed
> > Linux.
> > -Proto
I'm no authority on the subject (I've learned most of what I know simply by
lurking this list and reading PHK's posts), but there are two pieces to
watchdog-- the kernel-side piece and a userland daemon that acts as a dead
man's switch. The userland watchdogd (or whatever linux's equivalent)
enables the kernel bits and sends a "I'm still running" message to the
kernel every few seconds. If the kernel doesn't get that message, it assumes
userland is broken and institutes a reboot. This is why you can test with a
kill -9 to the watchdogd program-- it doesn't have time to deactivate the
in-kernel watchdog component before it dies.
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