This article will help to find the cause of the boot failure.
After bootup/upgrade the host fails to exit the maintenance mode. User can also observe:
"A critical failure was detected during system boot. The host cannot currently run workloads. Please refer to KB 93107 for more details."
#esxcli system maintenanceMode set -e=0
A general system error occurred: Cannot exit maintenance mode due to failure during boot.
There could be different reasons for the boot failure.
Example: failed to repartition the disk while upgrading from 6.5/6.7 to 8.0U2.
To find the cause of the boot failure login to the host and look for the relevant alert message in /var/run/log/vmkwarning.log file and follow the KB mentioned in it. The same alert message can be found on the sysAlert shell (press fn+option+f11) on ESXi DCUI.
Example: 2023-06-15T09:59:20.467Z Al(177) vmkalert: cpu0:1000079885)ALERT: An error occurred while backing up VFAT partition files before re-partitioning. This might be due to VFAT corruption, please refer to KB 91136 for steps to remediate the issue.
The workaround would be specific to the cause of the boot failure. Please refer to the KB specific to the failure.