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1b1ed1a
(Get the code!)
We have noticed that the upgrade from 12.04 to 14.04 has resulted in daemons that are started from rc.d scripts sometimes being run twice.
We've tracked this down to a race condition in the failsafe script. Here is the normal sequence of events:
Mar 16 10:39:37 failsafe: Failsafe of 120 seconds reached.
Mar 16 10:39:37 failsafe: net-device-up start event emitted
Mar 16 10:39:37 failsafe: starting failsafe script
Mar 16 10:39:37 failsafe: sleeping in failsafe script
Mar 16 10:39:37 failsafe: static-network-up start event emitted
Mar 16 10:39:37 failsafe: rc-sysinit starting event emitted
Mar 16 10:39:37 kernel: [ 2.056689] init: failsafe main process (642) killed by TERM signal
(Note the inaccurate message about the 120 seconds being reached which is actually logged immediately on boot - best just to ignore that. The TERM warning is also harmless - that is the normal result.)
Here is what we see on a bad boot, where the rc.d scripts are started twice:
Mar 16 10:24:47 failsafe: static-network-up start event emitted
Mar 16 10:24:47 failsafe: rc-sysinit starting event emitted
Mar 16 10:24:47 failsafe: Failsafe of 120 seconds reached.
Mar 16 10:24:47 failsafe: net-device-up start event emitted
Mar 16 10:24:47 failsafe: starting failsafe script
Mar 16 10:24:47 failsafe: sleeping in failsafe script
Mar 16 10:26:47 failsafe: emitting from failsafe script
Mar 16 10:26:47 failsafe: rc-sysinit starting event emitted
Mar 16 10:26:47 kernel: [ 122.229597] init: failsafe main process (797) killed by TERM signal
rc-sysinit has been emitted twice.
Note that the rc-sysinit event has been emitted before the failsafe script has been emitted, because in this boot it happens that the static-network-up event was emitted before the net-device-up event.
As a result, the normal stop on "starting rc-sysinit" rule in the failsafe job definition doesn't work because the failsafe job is not yet running.
Another way to look at the issue is that the rc-sysinit job definition's "start on (filesystem and static-network-up) or failsafe-boot" means that it will always start twice if it finishes before the failsafe handler fires.