VirtualBox mounts the same ISO in multiple virtual CD/DVD drives.

[mpack]

Related discussion topic, with logs. ​https://forums.virtualbox.org/viewtopic.php?f=8&t=98545

We've actually been seeing this error for years, but I can't find a ticket for it.

Users sometimes get confused and add a new CD/DVD drive to the VM recipe, instead of adding media to a drive.

If they do that while the GAs ISO is mounted in CD drive #1, then I believe that the next time they choose "Insert Guest Additions CD" in a running VM, VirtualBox sees the empty drive and inserts a second copy of the GAs ISO in drive #2, not noticing that drive #1 still holds a copy. That leaves you with the same media mounted in two CD drives, which obviously could never happen in the physical world. VirtualBox gets more confused from there, and users sometimes compound the problem by having this invalid state recorded in past snapshots. Once this happens the only known workaround is to manually edit the .vbox file.

Obviously, it should never be possible to mount the same media in more than one CD/DVD drive. I can think of a multitude of trivially easy ways to stop that happening, so I'm sure you will too.

Logs can be found in the linked discussion topic.

[Frank Batschulat (Oracle)]

Replying to mpack:

Obviously, it should never be possible to mount the same media in more than one CD/DVD drive. I can think of a multitude of trivially

fwiw, if the media is treated as a CD-ROM then it is a R/O device/media and mounted using a R/O file system iso9660 and as such can be mounted as many times as you want from the host onto different guest devices. This is different from say UDF, which would be a R/W file system accessing a DVD drive/media which is a R/W device/media modulo the case where you mount the media in it as a R/O ISO media using the UDF ISO bridge.

[fth0]

Ok, for the moment let's ignore the question if it is allowed to mount the VirtualBox Guest Additions ISO to several virtual drives simultaneously.

But: If you have managed to create this state (which is in fact as easy as mpack believes), the VirtualBox Manager doesn't allow you to resolve your problem, by greying out most of its actions (including Settings). So you have to resort to methods unknown (and not recommended) to the common user, like editing the .vbox file by hand. That's the real problem in my POV.

[mpack]

Replying to fbatschu:

fwiw, if the media is treated as a CD-ROM then it is a R/O device/media and mounted using a R/O file system iso9660 and as such can be mounted as many times as you want

I'm not entirely sure what you think this ticket is about, but that isn't it. The passage you quoted says only that you can't have the same CD inserted in two CD drives at the same time, as it's physically impossible. Not everyone is from Linux land, so don't assume I'm using Linux jargon when I use the common English word "mount".