Date: Sat, 3 Feb 1996 11:43:44 -0500 From: dennis@etinc.com (dennis) To: hackers@freebsd.org Subject: Re: Watchdog timers Message-ID: <199602031643.LAA25204@etinc.com>
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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. Unfortunately, in LINUX most of the hangs seem to be due to interrupt hangs. Its also nice to be able to customize the criteria for reboot. For example we had someone who had a HDD controller that failed occationally (didnt actually hang the system)...so they did sanity tests on it and rebooted when it failed (which is really a demand reset rather than a watchdog function). We've found that most of the people that want WDTs have machines that don't reboot reliably for one reason or another or require a hard reset, particularly those with remote systems and they dont want to take the chance on a soft reset. dennis ---------------------------------------------------------------------------- Emerging Technologies, Inc. http://www.etinc.com Synchronous PC Cards and Routers For Discriminating Tastes. 56k to T1 and beyond. Frame Relay, PPP, HDLC, and X.25 for BSD/OS, FreeBSD and LINUX.
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