wdt(7)                           DG/UX R4.11                          wdt(7)


NAME
       wdt - watchdog timer driver

DESCRIPTION
       This manual page describes the interface for the watchdog timer
       device driver for users such as the failovermon(1M).  The watchdog
       timer driver is used to help increase system availability.  The
       driver assists user-level monitoring programs in detecting higher
       level hangs.  Periodically the user performs a series of operations
       to insure the proper functioning of the system and informs the driver
       the completions of the operations.  However, when the user is unable
       to complete its operations and/or to communicate with the driver, the
       driver initiates a system halt to end the system hang.  Depending on
       the system setups, the system can reboot automatically upon the halt.
       The watchdog timer can be a valuable instrument in increasing system
       availability of unattended systems.

       The device is accessed using the standard open, close, and ioctl.

       The open system call provides a handle to access the watchdog timer
       driver.  The driver allows access to only one user.

       The close system call frees the handle to the watchdog timer driver
       established by open.

       The ioctl system call has the following form:

            int ioctl(fildes, command, argument);
            int     fildes;
            int     command;
            int     argument;

       and where command is:

       DGWDTMONITORSET
              Halts the system unless another DGWDTMONITORSET ioctl is
              sent within the number of seconds specified in argument.  If a
              zero is specified no further ioctl is necessary to keep the
              system from halting.

       Upon opening the wdt, the user continually send ioctls specifying the
       time of the next ioctl and performs its set of monitoring operations
       between ioctls.  After sending the first ioctl to inform the driver
       when to expect the second ioctl, the user then performs its
       monitoring operations and sends the second ioctl.  If the second
       ioctl arrived within the time specified by the first one, this
       process continues.  Otherwise, the driver halts the system because
       the expected ioctl failed to arrive in time.  The process can be
       terminated by closing the wdt or sending an ioctl with zero as its
       argument before the current ioctl expires.

FILES
       /dev/wdt                              wdt device node
       /usr/include/sys/intdgwdtioctl.h  watchdog timer ioctl commands

SEE ALSO
       failovermon(1M), ioctl(2).

NOTE
       Depending on the system hardware configuration, wdt can also be the
       device driver for the physical watchdog timer. The physical watchdog
       timer ensures the proper functioning of the innermost portion of the
       system (hardware and software).  If for any reason the system
       experiences a hard hang (i.e. the innermost portion of the system no
       longer functions), the watchdog timer resets the system.  If the
       autoboot feature is enabled, the system will reboot immediately
       without any operator intervention.

       On some DG/UX systems an enhanced watchdog timer will attempt to halt
       the system via a non-maskable interrupt.  If autodump is enabled, the
       system will attempt to take a memory dump.  If autoboot is enabled,
       the system will reboot without user intervention after taking the
       dump.  If the system does not respond to the non-maskable interrupt,
       the watchdog timer proceeds to reset the system as described above.


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