please help, my server does not boot after forced reboot

[lia]

Hi, I have installed LAPM with VirtualBox. But it does not boot after forced reboot.
When I try to boot it using my snapshots (I have 11 snapshots), it just shows an error: no bootable medium found.
I googled the error and saw a lot of guides for this.
But if I insert the .iso file that I used before, it starts the linux installation again over the snapshot, which means it will be overwritten on my datas.
I really don't know what I have to do.
I have attached the details of my system. Can anyone help me with this problem?

[mpack]

Best guess: you never actually installed Ubuntu, you were just running in the non-persistent "live cd" (demo) mode. Shutting down the VM will cause any changes to be lost.

p.s. Regarding the VM you created, I'd have thought that 15GB was quite a small disk for any modern OS. Why so small?

Please provide a VM log file. With the VM fully shut down, right click it in GUI. Select "Show Log" and save "VBox.log" (ONLY) to a zip file. Attach the zip here.

[lia]

Hi, I have attached a zip and a screenshot of my snapshots.
After checking my snapshots, I realized only the last 2 snapshots (marked with the red box) are corrupted.
I have successfully restored the system with the third snapshot from the end of the list below, but the problem is that it does not have my files because I made this snapshot just after finishing the LAPM installation.
My files are only on the 2 corrupted snapshots... Is there any hope?

[mpack]

I see no evidence of a corrupted snapshot. If a snapshot was corrupted the VM would either refuse to start at all (not to be confused with the guest OS not booting), or you'd get a crash later on. There should be no reason why the boot sectors should be rewritten to any snapshot, so a damaged snapshot is unlikely to lead to a guest OS boot failure.

So, backing up. I see no evidence of a boot failure. I do see strange things about the VM, such as two CD drives (both empty), and a small hdd.

However, we can dig deeper. On that front: showing me a picture of the names you given to the snapshots doesn't actually tell me very much. Much more telling would be a directory listing of the VM folder AND the snapshots subfolder. What I want to see is the size in bytes of the VDI files and .sav files that might be in those folders.

[lia]

Hi, mpack. Thank you for your reply.
I have attatched the screenshots of my VM folder. I think that the "{ecd36463-06ad-4546-8a7f-7d91b29fa16b}.vdi" is the one I failed to boot.
And about the HDD size, I saw some post that the CentOS wll take up only 4GB, and VirtualBox suggested 8GB as a default when I started installing it.
So I thought that it will be enough.

[mpack]

Hmm. Well, you do seem to have data in the snapshots, so it's unlikely that you were running in safe mode.

However the current snapshot VDI is only 2MB, which means it's just a header - it doesnt have any data in it. I suggest that you back up the entire VM folder (so things can't get any worse), and then with the VM shut down, revert to next older snapshot.

Some tips: I suggest that if you want a robust system (and meanwhile save yourself a huge amount of disk space), then you need to stop using snapshots. I also suspect that your base disk is fixed size, and fixed size base + snapshots is pointless (any argument for fixed size is negated if snapshots are used). If you want robustness, clone the VM to a normal one (no snapshots). Use backups to main a selection of states. Snapshots are not backups.