NAME

     watchdog — hardware and software watchdog

SYNOPSIS

     #include <sys/watchdog.h>

DESCRIPTION

     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_* below).

     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)

RETURN VALUES

     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.

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 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.

SEE ALSO

     watchdogd(8), watchdog(9)

HISTORY

     The watchdog code first appeared in FreeBSD 5.1.

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>.

BUGS

     The WD_PASSIVE option has not yet been implemented.