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Hardware and software watchdog.

December 21, 2009
WATCHDOG(4) BSD Kernel Interfaces Manual WATCHDOG(4)


watchdog — hardware and software watchdog


#include <sys/watchdog.h>


The watchdog facility is used for controlling hardware and software watchdogs. The device /dev/fido responds to a single ioctl(2) call, WDIOCPATPAT. It takes a single argument which represents a timeout value specified as a power of two nanoseconds, or-ed with a flag selecting active or passive control of the watchdog. WD_ACTIVE indicates that the watchdog will be kept from timing out from userland, for instance by the watchdogd(8) daemon. WD_PASSIVE indicates that the watchdog will be kept from timing out from the kernel. The ioctl(2) call will return success if just one of the available watchdog(9) implementa‐ tions supports setting the timeout to the specified timeout. This means that at least one watchdog is armed. If the call fails, for instance if none of watchdog(9) implementations support the timeout length, all watchdogs are disabled and must be explicitly re-enabled. To disable the watchdogs pass WD_TO_NEVER. If disarming the watchdog(s) failed an error is returned. The watchdog might still be armed!


The ioctl returns zero on success and non-zero on failure. [EOPNOTSUPP] No watchdog present in the kernel or none of the watchdogs supports the requested timeout value (timeout value other than 0). [EOPNOTSUPP] Watchdog could not be disabled (timeout value of 0). [EINVAL] Invalid flag combination passed.


#include <paths.h> #include <sys/watchdog.h> #define WDPATH "/dev/" _PATH_WATCHDOG int wdfd = -1; static void wd_init(void) { wdfd = open(WDPATH, O_RDWR); if (wdfd == -1) err(1, WDPATH); } static void wd_reset(u_int timeout) { if (ioctl(wdfd, WDIOCPATPAT, &timeout) == -1) err(1, "WDIOCPATPAT"); } /* in main() */ wd_init(); wd_reset(WD_ACTIVE|WD_TO_8SEC); /* potential freeze point */ wd_reset(WD_TO_NEVER); Enables a watchdog to recover from a potentially freezing piece of code. options SW_WATCHDOG in your kernel config adds a software watchdog in the kernel, dropping to KDB or panic-ing when firing.


watchdogd(8), watchdog(9)


The watchdog code first appeared in FreeBSD 5.1.


The watchdog facility was written by Poul-Henning Kamp <>. The software watchdog code and this manual page were written by Sean Kelly <>. Some contributions were made by Jeff Roberson <>.


The WD_PASSIVE option has not yet been implemented.
BSD December 21, 2009 BSD
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