snapshots / disposable VMs

[ThomasWaldmann]

I'm used to use Qubes OS on my other machine, especially using disposable VMs for random web surfing or potentially dangerous stuff (like working with files from untrusted sources).

A disposable VM is a VM created from a given state (template VM), executes normally, but when shut down, all changes get thrown away. E.g. if you do web surfing, you do not have to worry about getting tracked long-term by cookies or similar mechanisms - or if you try installing random software just to have a quick look, you do not have to worry about spoiling your system somehow, because all state will get thrown away automatically at shutdown time. Also malware does not have a chance to persist.

Such a dispVM could be implemented with qemu temporary snapshots.

Normal snapshots would be also useful as a safety net, e.g. before running OS upgrades or critical SW installations inside your VMs. If anything goes wrong, one can just revert to a known-good state in a snapshot.

[ThomasWaldmann]

BTW, oracle virtualbox has a GUI for managing snapshots.

[juanandresgs]

Looks like #3067 is inching us closer. Any chance we can get a snapshot management view? This would be hugely valuable.
Willing to donate to support dev.

[ktprograms]

Hi @juanandresgs, what do you mean by a snapshot management view?

BTW the PR is only for temporary snapshots, not qcow2 snapshots with backing files.

[ThomasWaldmann]

@ktprograms if you have virtualbox installed somewhere, just have a look at its snapshots dialogues.

One can create (permanent) snapshots there, go back to the state of some snapshot, delete/merge snapshots, etc.

[ktprograms]

I just realised, QEMU seems to have 3 kinds of snapshots.

1. Using the -snapshot option for a temporary disposable VM.
2. qcow2 backing files to have multiple images based on a single 'parent' image.
3. qcow2 save states which you can create and revert back to using the qemu-img snapshot subcommand.

If I understand it, you would like (3) to be implemented, right?

[ThomasWaldmann]

Well, guess we need 1 and 3.

2 would be also nice to have as a space saver maybe.

[ktprograms]

@osy as I understand from the Git history, directly using qemu-img as a dylib was removed due to some problem on iOS, right? These snapshot features would be a lot easier to implement by calling qemu-img instead of implementing it from scratch. What was the problem on iOS and is there any solution?

[juanandresgs]

Definitely thinking (3). I've added the picture of the snapshot manager from VMWare Fusion for reference.

[jimmont]

@ktprograms I'm looking to use "2." using snapshot against a backing file and "3." save states (I assume this is like virtualbox, or perhaps I need to read up on it). I attempted to setup 2 manually using qemu-img and UTM's image structure and when changing the settings from the parent to the snapshot the parent image is automatically deleted losing my setup entirely.

[ktprograms]

@jimmont I'm sorry to hear that it deleted your disk images, that happened to me when I was testing (2) as well. It seems that if you mess with the drives (create new ones or move/resize old ones) manually from the command line while UTM is still open, then it deletes the drives. If you have closed UTM first, then you can try and create the new disk images with backing files, but I find the other problem is that the backing file can't be properly accessed if it isn't in the same folder as the new image, so the (temporary) solution I came up with is to hard link the backing file into each VM folder.

However, please note that this is not a supported configuration and (as you have found out) runs the risk of you losing data.

(3) would be implemented by either directly using qemu-img snapshot ... or by using whatever internal mechanism qemu-img snapshot ... uses.

[rvaliev]

The ability of making snapshots will be very nice feature for the users whose workflow relies on on VirtualBox and want to move to the M1 devices. (both UI and command line functionality)

[juanandresgs]

Is there a dev interested in implementing this? We can start a donation drive 🆘

[ghost]

+1 from me. This is a highly important feature, especially when you want to install software that is non-trivial to install and highly probable to fail. You can then revert back to a safe state, and retry.

From Parallels and VirtualBox I know their handling, and that's what should be provided here as well (as described above with the screenshot from @juanandresgs .

In the meantime: I tried to use qemu directly to create snapshots, but for unknown reasons this did not work (qemu does not recognize the machine). Am I doing something wrong, or is there an incompatibility?

[ktprograms]

Hi @innoreq, can you please share the debug log / error alert because I don't understand what you mean by qemu does not recognise the machine?

The reason why this feature isn't very easy to implement is because, for iOS compatibility, the qemu-img command cannot be used.

Manually replicating the qemu-img snapshot command wouldn't be simple and would be highly likely to be incorrect in some way and corrupt the disk image.

Currently, the best solution is to Clone your VMs, and because they are copied using APFS Copy on Write clones, it will not use extra space until you start changing one of the VMs, at which point the amount of space used will be the delta between the original and the second VM. For more information you can look at man 2 clonefile and the -c option of the macOS cp command.

Note that even though it's a Copy on Write clone, you can freely use either VM (it won't break if you start using / modifying the original VM, even if you use both at the same time).

[marcelloromani]

I ended up here as I was also looking for something similar to VBox's snapshot management.
I realised with the current UTM functionality it's pretty easy to get the same end result.
I created a new Ubuntu machine, installed all the basic packages I needed for my tests and other files (public keys for passwordless logins, etc.). I named this machine "Template".

Whenever I need to test something on the machine, I simply clone the Template machine into what I consider a disposabile test machine (e.g. "Test1"), start it work on it. The only thing to lookout for is ensuring I don't accidentally start the Template machine (which would change the state of the disk image).

When I'm done, I simply delete the Test1 machine and create a new clone.

[ktprograms]

Now that qemu-img is being built as a shared library and is usable from code on macOS (see b65c9f6), it should be possible to implement this.

@osy Can you confirm that this is correct?

[osy]

Yes I plan to add other qemu-info functionalities as well. But right now it only works on macOS because we can launch new processes. On iOS you can call it once but if you run it again it errors.

[ktprograms]

@osy I can work on implementing save states using qemu-img snapshot this week, but FYI my other suggestion for multiple qcow2 images based off a backing file won't be doable yet until #3227 is merged (that will allow the backing file to just be stored as a bookmark file for each VM while the real backing image can be stored elsewhere).

[ktprograms]

On iOS you can call it once but if you run it again it errors.

What exactly is the error? Just wondering.

[osy]

Don't remember you can try it. It basically doesn't like main called multiple times.

[henry2man]

Hi there. Does anybody tried this project? https://github.com/Metamogul/UTM-Snapshot-Manager

[gitsnaf]

Hi there, is there any progress regarding a snapshot manager? I would also very much appreciate it if there was such a functionality.

[juanandresgs]

Plez?

[dataprolet]

Plez?

What do you mean?

[osy]

Disposable VMs have been available for QEMU backend for multiple releases now. #5484 will track the feature request for snapshots.