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.
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