Date: Fri, 2 Feb 1996 11:20:24 +0100 (MET) From: J Wunsch <j@uriah.heep.sax.de> To: freebsd-hackers@freebsd.org (FreeBSD hackers) Subject: Re: Watchdog timers Message-ID: <199602021020.LAA04930@uriah.heep.sax.de> In-Reply-To: <199602011921.LAA23294@bluewhale.emergent.com> from "Curt Mayer" at Feb 1, 96 11:21:04 am
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As Curt Mayer wrote: > > > hey, guys. here's a solution that smells much more like unix. > have a daemon running on each node that is prone to hangup. > this process wakes up every once in a while and does a system checkup. > (stats things, pings places, looks at kernel statistics). when it see > that things are ok, it sends a datagram to a particular machine, > > this node, the monitor, has a table in memory of all recent datagrams > from each node. when a node hasn't been heard from for a while, it > tells a BSR x10 controller to cycle power on the hung node. DUH. Idea stolen from Linux: create a /dev/watchdog for this purpose. Once it is held open by a process, the kernel resets the CPU if it doesn't get a response on a device after a certain time. The idea behind this is that most of the hanging systems have still a running async portion of the kernel, i.e. things like interrupt handling continue to work, but the process context switching hangs for some reason (e.g. SCSI bus hangs etc.). The chances are good that the kernel could still kill itself. Not ideal, but also no cost. -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)
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