NAME¶
wdmd - watchdog multiplexing daemon
SYNOPSIS¶
wdmd [OPTIONS]
DESCRIPTION¶
This daemon opens /dev/watchdog and allows multiple independent sources to
detmermine whether each KEEPALIVE is done. Every test interval (10 seconds),
the daemon tests each source. If any test fails, the KEEPALIVE is not done. In
a standard configuration, the watchdog timer will reset the system if no
KEEPALIVE is done for 60 seconds ("fire timeout"). This means that
if single test fails 5-6 times in row, the watchdog will fire and reset the
system. With multiple test sources, fewer separate failures back to back can
also cause a reset, e.g.
T seconds, P pass, F fail
T00: test1 P, test2 P, test3 P: KEEPALIVE done
T10: test1 F, test2 F, test3 P: KEEPALIVE skipped
T20: test1 F, test2 P, test3 P: KEEPALIVE skipped
T30: test1 P, test2 F, test3 P: KEEPALIVE skipped
T40: test1 P, test2 P, test3 F: KEEPALIVE skipped
T50: test1 F, test2 F, test3 P: KEEPALIVE skipped
T60: test1 P, test2 F, test3 P: KEEPALIVE skipped
T60: watchdog fires, system resets
(Depending on timings, the system may be reset sometime shortly before T60, and
the tests at T60 would not be run.)
A crucial aspect to the design and function of wdmd is that if any single source
does not pass tests for the fire timeout, the watchdog is guaranteed to fire,
regardless of whether other sources on the system have passed or failed. A
spurious reset due to the combined effects of multiple failing tests as shown
above, is an accepted side effect.
wdmd will exit if a watchdog driver is not loaded.
wdmd cannot be used on the system with any other program that needs to open
/dev/watchdog, e.g.
watchdog(8).
Test Source: clients¶
Using libwdmd, programs connect to wdmd via a unix socket, and send regular
messages to wdmd to update an expiry time for their connection. Every test
interval, wdmd will check if the expiry time for a connection has been
reached. If so, the test for that client fails.
(Other test sources such as scripts executed each test interval may be added in
the future.)
OPTIONS¶
- -D
- Enable debugging to stderr and don't fork.
- -H num
- Enable (1) or disable (0) high priority features such as
realtime scheduling priority and mlockall.
Default 1.