This is OS hang-up issue (see also Fig.1).
Figure 2 shows it occurred around 20:37 JST.
GR-Y flash is somehow still alive according to Fig.3.
Possible recovery procedure
1. Request SAFE or DOWN for all guardian nodes except VIS-SR3
2. Pause VIS-SR3
3. Disable Dolphin connection of K1SR3
4. Reboot SR3 front-end from BMC interface.
IFO has been now handed over to Kenta and an initial alignment work is in progress.
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SAFE was requested for all suspension except Type-A (Type-A is Dolphin free node) at first.
And also, VIS_SR3 and LSC_LOCK guardians were paused.
Then K1SR3 was rebooted after disconnecting it from the Dolphin network.
Though rebooting process was failure in several times due to missing DAC card, Dolphin card, etc., K1SR3 finally came back online.
After recovering a front-end computer, I reverted paused guardian nodes and requested LOCK_ACQUISITION to VIS_SR3.
Recovering the front-end computer was completed at 10:00.
GR-Y flash was also came back after requesting LOCK_ACQUISITION to VIS_BS and/or VIS_SR2.
After the recovering work of the front-end computer, Kenta started the initial alignment procedure.
But large EQ occurred during the procedure.
We are now waiting.