virtualbox.org

I guess I wasn't clear...

..."/media/dans/working" is NOT shared in the Linux host, like so: It's only mounted in Linux host and then attachment/share is configured in VB.

What you show in the second picture is a "true" network share. What you showed in the first picture is the VirtualBox shared folder, a very simplistic way of presenting a filesystem to the guest with the contents of that "share". Look at the user manual, Ch. 4.3. Shared folders for more details.

Ok.....as for checking the hard drive, that's been done several times with GParted (using a live USB), GSmartcontrol and from the Windows 10 dual-boot side. Nothing found.

Is it your opinion, based on your previous, that this is simply coincidental with running VB/VM?

I think so. I can't see the connection. VirtualBox is merely another simple application asking for stuff in your host's filesystem, be it folders, or files, or attributes of those two. It doesn't have any special kernel drivers for that purpose on the host side. I can't see how a user-space application can screw up your MBR.

All right then---VM's been running without the shared folder/drive for several days without incident. Albeit it's a pain in the butt, I'm gonna try to duplicate and take pics of the screen with my phone, convert to jpeg and upload.......

Well, it did it again in short order --- crashed with pop up, altered Linux host permissions (read only I think) and wiped out the MBR.
Error pop up on freeze:

I can't find the FAQ for uploading pics and I'm stopped at this point...

...essentially it's as I have stated previously: when the VM is connecting to "/media/dans/working" after a random period the VM/VB crashes and Linux IS altered. I've run all sorts of disk checking and even took it to a PC repair place to check it. The hard drive reports no problems. Now, since this crash and wiping out of the MBR "only" happens when "/media/dans/working" is attached to the guest and the host partition winds up with altered permissions along with the MBR no longer good. What conclusion can we come to?

And now, after repairs it seems that the VM in VB is gone:

What is your evidence that VirtualBox is the cause of this problem and not simply the victim?

If you aren't using raw disk then there's simply no mechanism that allows VirtualBox to damage the host MBR, not even a buggy mechansm.

VirtualBox is a host app. It can't do anything to the host that any other host app can't do.

The missing start tag error is an indication of the vbox file becoming corrupt. This usually happens when the guest is shut down hard ( crashed ), and repairable by copying the vbox-prev to the vbox file.
Not sure about the rest of this topic.

mpack wrote:What is your evidence that VirtualBox is the cause of this problem and not simply the victim?

If you aren't using raw disk then there's simply no mechanism that allows VirtualBox to damage the host MBR, not even a buggy mechansm.

VirtualBox is a host app. It can't do anything to the host that any other host app can't do.

While I admit that I'm not a PC guru I know my way around logic...

...if a particular event repeats itself and one removes one of the actions/actors from conditions/context and that event then ceases one must conclude that, that which was removed from the context does not interact well with the set conditions.

This event has NEVER occurred to me nor this laptop in the past --- been running 17.3 since it was released. When I run VB/VM for weeks without using the shared folder condition it NEVER crashes --- it only crashes when I have the VM connect to the Linux mount "/media/dans/working". Is that considered raw disk access? Could you give me an example of raw disk access? I've read the manual regarding that and it's just not clear to this tired mind without a configuration example.

Raw disk access means in a sense that you're accessing directly the hardware, the key components of the hard disk (like the MBR, and every other sector) directly, without the protections that the host OS has in place to prevent stupidity from kicking in. It assumes that you know exactly what you're doing and exactly how things are done. You could destroy your MBR and your whole HD that way.

Shared folders is NOTHING close to that. You go through two layers of security/protection. So it is not technically possible to do what you're describing, even if that is your goal. You don't have access to that piece of information.

Why it happens, what triggers it, that's another story altogether. We know for sure that it can't happen the way that you're describing it. No way.

socratis wrote:We know for sure that it can't happen the way that you're describing it. No way.

Why would you say that when it is happening? I've included all that has been asked and have run several tests --- it only occurs when the VM attaches to /media/dans/working which is an NTFS data partition in the Windows side of the dual boot --- it never occurs when that attachment is not made. Are there any other logs or reports that I could put up to help on this thing?

Again, could you give me a specific example of raw disk access --- how would a VM go about doing that?

The problem lies most probably in the NTFS filesystem driver of your Linux host system.
Virtualbox just triggers the problem when crashing the system, but every other similar crash of your Linux host would probably create the same problem.

Hey, that makes sense, thank you --- how to I go about updating/changing that driver?

old-man wrote:Why would you say that when it is happening?

Because by using the VirtualBox shared folders you don't have access to the MBR, not even read-only. Even if you had raw disk access to the Windows partition, you still wouldn't have access to the MBR, it's a different part.

old-man wrote:Again, could you give me a specific example of raw disk access --- how would a VM go about doing that?

Take a look at the manual, ch. 9.9.1. Using a raw host hard disk from a guest. Don't do it unless you know exactly what you're doing. If you lose data that way, the only thing I can do is not even being sorry, but only a "I told you".

PS. I'm starting to believing that Martin's idea may have a lot of merit.