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.TH WD 3
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.SH NAME
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wd - hardware watchdog timer
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.SH SYNOPSIS
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.nf
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.B bind -a #w /dev
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.sp 0.3v
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.B /dev/wdctl
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.SH DESCRIPTION
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This device presents textual information about hardware watchdog timers
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on PCs and some other machines,
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and allows user-level control of them.
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When enabled, a watchdog timer counts to zero in a few seconds;
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upon reaching zero, it resets the machine with an NMI or equivalent.
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Some process must periodically restart the watchdog to avoid the NMI and
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keep the system alive;
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.IR watchdog (8)
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is one such program.
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.PP
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Reads from
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.I wdctl
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yield data of this form:
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.IP
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.EX
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enabled 3 restarts
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.EE
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.LP
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or
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.IP
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.EX
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disabled 3 restarts
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.EE
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.LP
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Control messages may be written to
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.I wdctl
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and include
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.LR enable ,
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.LR disable ,
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and
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.LR restart .
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.LP
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The watchdog is disabled at system shutdown, and when the last open
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file descriptor for
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.I wdctl
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is closed.
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.SH SOURCE
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.B /sys/src/9/port/devwd.c
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.br
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.B /sys/src/9/*/*watchdog.c
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.SH SEE ALSO
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.IR proc (3),
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.IR watchdog (8)
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.SH BUGS
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On PCs,
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to ensure consistent use of one CPU's timers,
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an
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.L enable
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message wires the issuing process
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(see
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.IR proc (3))
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to a CPU,
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and any subsequent control messages will
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wire the issuing processes to that same CPU.