watchdog man page on OpenBSD

Man page or keyword search:  
man Server   11362 pages
apropos Keyword Search (all sections)
Output format
OpenBSD logo
[printable version]

WATCHDOG(4)		  OpenBSD Programmer's Manual		   WATCHDOG(4)

     watchdog - hardware timers/counters for quick crash recovery

     Hardware watchdog timers are devices that reboot the machine when it
     hangs.  The kernel continually resets the watchdog clock on a regular
     basis.  Thus, if the kernel halts, the clock will time out and reset the
     machine.  Watchdog timers may be configured to be reset from userland to
     cause a reboot if process scheduling fails; see watchdogd(8) for further

     A number of hardware watchdogs are supported, and all are configured
     using sysctl(8) under the kern.watchdog name:	 Automatically reset (`tickle') the watchdog
				 timer but disable it at system shutdown time.

	   kern.watchdog.period	 The timeout in seconds.  Setting it to zero
				 disables the watchdog timer.

     In situations where the machine provides vital services which are not
     handled completely in kernel space, e.g. mail exchange, it may be
     desirable to reboot the machine if process scheduling fails.  This is
     done by setting to zero and running a process which
     repeatedly sets kern.watchdog.period to the desired timeout value.	 Then,
     if process scheduling fails, the process resetting the timer will not be
     run, leading to the machine being rebooted.  Note that the kernel will
     not automatically disable an enabled watchdog at system shutdown time
     when is set to zero.

     Watchdog timers should be used in high-availability environments where
     getting machines up and running quickly after a crash is more important
     than determining the cause of the crash.  A watchdog timer enables a
     crashed machine to autonomously attempt to recover quickly after a system

     Note that this also means that it is unwise to combine watchdog timers
     with ddb(4) since the latter may prevent the former from resetting the
     watchdog timeout before it expires.  This means that the machine will be
     rebooted before any debugging can be done.	 In other words: For mission
     critical machines, disable ddb(4) by adding ``ddb.panic=0'' to
     sysctl.conf(5) since this will give the chance to perform a crash dump
     and reboot.  Simply setting the watchdog will lose the debug trace of
     what went wrong.

     ddb(4), sysctl.conf(5), config(8), sysctl(8), watchdogd(8)

     For systems with multiple watchdog timers available, only a single one
     can be used at a time.  There is currently no way of selecting which
     device is used; the first discovered by the kernel is selected.

OpenBSD 4.9			 May 21, 2009			   OpenBSD 4.9

List of man pages available for OpenBSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net