WD(3)                                                       WD(3)

     NAME
          wd - hardware watchdog timer

     SYNOPSIS
          bind -a #w /dev
          /dev/wdctl

     DESCRIPTION
          This device presents textual information about hardware
          watchdog timers on PCs and some other machines, and allows
          user-level control of them.  When enabled, a watchdog timer
          counts to zero in a few seconds; upon reaching zero, it
          resets the machine with an NMI or equivalent.  Some process
          must periodically restart the watchdog to avoid the NMI and
          keep the system alive; watchdog(8) is one such program.

          Reads from wdctl yield data of this form:

               enabled 3 restarts

          or

               disabled 3 restarts

          Control messages may be written to wdctl and include
          `enable', `disable', and `restart'.

          The watchdog is disabled at system shutdown, and when the
          last open file descriptor for wdctl is closed.

     SOURCE
          /sys/src/9/port/devwd.c
          /sys/src/9/*/*watchdog.c

     SEE ALSO
          proc(3), watchdog(8)

     BUGS
          On PCs, to ensure consistent use of one CPU's timers, an
          `enable' message wires the issuing process (see proc(3)) to
          a CPU, and any subsequent control messages will wire the
          issuing processes to that same CPU.