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     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)
     implementations 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
                   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() */
           /* potential freeze point */

     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.