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NAME

     watchdog - hardware and software watchdog

SYNOPSIS

     #include <sys/watchdog.h>

DESCRIPTION

     The watchdog facility is used for controlling hardware and software
     watchdogs.

     /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!

RETURN VALUES

     The ioctl returns zero on success and non-zero on failure.

     [EOPNOTSUPP]       No watchdog present in the kernel (timeout value other
                        than 0).

     [EOPNOTSUPP]       Watchdog could not be disabled (timeout value of 0).

     [EINVALID]         Invalid flag combination passed.

     [EINVALID]         None of the watchdogs supports the requested timeout
                        value.

EXAMPLES

           #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.

SEE ALSO

     watchdogd(8), watchdog(9)

HISTORY

     The watchdog code first appeared in FreeBSD 5.1.

BUGS

     The WD_PASSIVE option has not yet been implemented.

AUTHORS

     The watchdog facility was written by Poul-Henning Kamp 〈phk@FreeBSD.org〉.
     The software watchdog code and this manual page were written by Sean
     Kelly 〈smkelly@FreeBSD.org〉.  Some contributions were made by Jeff
     Roberson 〈jeff@FreeBSD.org〉.