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.

Debian                                           January 2, 2018                                     WATCHDOG(4)