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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 supports several optional ioctl(2) calls for configuration, and
     responds to a single operational ioctl 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 WDIOCPATPAT 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.  By default, this will be a hardware watchdog if one is
     present, but if no hardware watchdog is able to process the request, a default software
     watchdog is enabled.  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 optional configuration ioctl commands are listed here, along with the type of the
     parameter used.  Examples of their use can be found in watchdogd(8).

     WDIOC_SETTIMEOUT int           set/reset the timer

     WDIOC_GETTIMEOUT int           get total timeout

     WDIOC_GETTIMELEFT int          get time left

     WDIOC_GETPRETIMEOUT int        get the pre-timeout

     WDIOC_SETPRETIMEOUT int        set the pre-timeout

     WDIOC_SETPRETIMEOUTACT int     Set the action when a pre-timeout occurs (see WD_SOFT_*

     WDIOC_SETSOFT int              Use an internal software watchdog instead of hardware.  There
                                    is also an external software watchdog, which is used by
                                    default if no hardware watchdog was attached.

     WDIOC_SETSOFTTIMEOUTACT int    Set the action whan a soft timeout occurs.

     The actions that may be specified for the pre-timeout or the internal software watchdog are
     listed here.  Multiple actions can be specified by ORing values together.

     WD_SOFT_PANIC  panic

     WD_SOFT_DDB    enter debugger

     WD_SOFT_LOG    log(9)

     WD_SOFT_PRINT  printf(9)


     The WDIOCPATPAT 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.

     The configuration ioctl operations return zero on success and non-zero on failure.


           #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 forces a software watchdog in the kernel to be configured even if a
     hardware watchdog is configured, dropping to KDB or panicking when firing, depending on the
     KDB and KDB_UNATTENDED kernel configuration options.


     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.