Lubuntu 20.0.4 fail to boot on Windows 10 Enterprise host

[zhiyazw]

VirtualBox 6.1.40
Host: Windows 10 Enterprise
Guest: Lubuntu 20.0.4

One day, An application IntelliJ in Lubuntu guest complained that it couldn't write, so I reboot the guest.
But it failed to boot up.
Every time it went to the Linux boot menu (choose boot option), it wouldn't before.
Then it hung in below screen.



I also tried reboot the host.

I've read the post HMR3Init: Attempting fall back to NEM (Hyper-V is active) (viewtopic.php?f=25&t=99390).
But the difference is, I didn't find the log line below it described.

{timestamp} HM: HMR3Init: Attempting fall back to NEM: VT-x is not available
{timestamp} NEM: WHvCapabilityCodeHypervisorPresent is TRUE, so this might work...

or

{timestamp} HM: HMR3Init: Attempting fall back to NEM: AMD-V is not available
{timestamp} NEM: WHvCapabilityCodeHypervisorPresent is TRUE, so this might work...

I haven't yet tried the steps in that post as I'm on a Windows 10 Enterprise host and lack of privilege and the symptom looks different.

pls find my log in attachment, could someone take a look to the log, see if there's any new issue.

[scottgus1]

The log was taken while the VM window was open, and the VM was only running for about 4 minutes, so some diagnostic info is missing, and a slow-boot VM cannot be ruled out.

Hyper-V is turned off, so no issues there.

An application IntelliJ in Lubuntu guest complained that it couldn't write

Could be that the VM's disk is filled up.

Ubuntu is known to go blackscreen if there is not enough free disk space to start the desktop environment. This happens in real PCs too. The solution is to log on text-only and delete stuff until the desktop environment can start. Web-search how to fix this in an Ubuntu PC and apply the steps to the VM. Also see How to Resize a Drive

[zhiyazw]

Finally, when I typed exist in initramfs, it told me my main disk got corrupted, I fixed it with fsck, then it came back normal now.
Why doesn't it tell me at first, which would save me one day...