ESXi host experienced an unexpected reboot with the event "Host had been powered off. Last reboot reason is unknown"

Products

• VMware vSphere ESXi

Issue/Introduction

• An abrupt reboot was recorded on the ESXi host.
• On the ESXi host , the below entries are logged in /var/run/log/hostd.log : 
  

  YYYY-MM-DDTHH:MM:SSZ info hostd[######] [Originator@####sub=Hostsvc.VmkVprobSource] VmkVprobSource::Post event: (vim.event.EventEx) {
  -->    key = ###,
  -->    chainId = #,
  -->    createdTime = "YYYY-MM-DDTHH:MM:SSZ",
  -->    userName = "",
  -->    host = (vim.event.HostEventArgument) {
  -->       name = "ESXi-Dell-###",
  -->       host = 'vim.HostSystem:ha-host'
  -->    },
  -->    eventTypeId = "esx.audit.host.poweroff.reason.unavailable",
  -->    objectId = "ha-host",
  -->    objectType = "vim.HostSystem",
  --> }
  YYYY-MM-DDTHH:MM:SSZ info hostd[######] [Originator@####sub=Vimsvc.ha-eventmgr] Event # : Host had been powered off. Last reboot reason is unknown. Please check ESXi and the BMC logs for further details. Please consult vSphere Documentation Center or follow the Ask VMware link for more information.

• The iDRAC hardware events report a message similar to the following : "The iDrac firmware was rebooted with the following reason: ac"

Environment

VMware vSphere ESXi 7.0.x

Cause

The Dell PowerEdge server was restarted because of an AC power supply issue.

Resolution

As this appears to be a hardware issue, coordinate with the hardware vendor to investigate further.