.TH WD 3
.SH NAME
wd - hardware watchdog timer
.SH SYNOPSIS
.nf
.B bind -a #w /dev
.sp 0.3v
.B /dev/wdctl
.SH 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;
.IR watchdog (8)
is one such program.
.PP
Reads from
.I wdctl
yield data of this form:
.IP
.EX
enabled 3 restarts
.EE
.LP
or
.IP
.EX
disabled 3 restarts
.EE
.LP
Control messages may be written to
.I wdctl
and include
.LR enable ,
.LR disable ,
and
.LR restart .
.LP
The watchdog is disabled at system shutdown, and when the last open
file descriptor for
.I wdctl
is closed.
.SH SOURCE
.B /sys/src/9/port/devwd.c
.br
.B /sys/src/9/*/*watchdog.c
.SH SEE ALSO
.IR proc (3),
.IR watchdog (8)
.SH BUGS
On PCs,
to ensure consistent use of one CPU's timers,
an
.L enable
message wires the issuing process
(see
.IR proc (3))
to a CPU,
and any subsequent control messages will
wire the issuing processes to that same CPU.