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DisposableVMs
A DisposableVM (previously known as a "DispVM") is a lightweight VM that can be created quickly and will disappear when closed. DisposableVMs are usually created in order to host a single application, like a viewer, editor, or web browser.
From inside an AppVM, choosing the Open in DisposableVM option on a file will launch a DisposableVM for just that file.
Changes made to a file opened in a DisposableVM are passed back to the originating VM.
This means that you can safely work with untrusted files without risk of compromising your other VMs.
DisposableVMs can be launched either directly from dom0's Start Menu or terminal window, or from within AppVMs.
While running, DisposableVMs will appear in Qubes VM Manager with the name disp####.
This diagram provides a general example of how DisposableVMs can be used to safely open untrusted links and attachments in DisposableVMs. See this article for more on why one would want to use a DisposableVM.
Security
If a DisposableVM Template becomes compromised, then any DisposableVM based on that DisposableVM Template could be compromised. In particular, the default DisposableVM Template is important because it is used by the "Open in DisposableVM" feature. This means that it will have access to everything that you open with this feature. For this reason, it is strongly recommended that you base the default DisposableVM Template on a trusted TemplateVM.
DisposableVMs and Local Forensics
At this time, DisposableVMs should not be relied upon to circumvent local forensics, as they do not run entirely in RAM. For details, see this thread.
When it is essential to avoid leaving any trace, consider using Tails.
DisposableVMs and Networking
Similarly to how AppVMs are based on their underlying TemplateVM, DisposableVMs are based on their underlying DisposableVM Template. R4.0 introduces the concept of multiple DisposableVM Templates, whereas R3.2 was limited to only one.
On a fresh installation of Qubes, the default DisposableVM Template is called fedora-XX-dvm (where XX is the Fedora version of the default TemplateVM).
If you have included the Whonix option in your install, there will also be a whonix-ws-dvm DisposableVM Template available for your use.
You can set any AppVM to have the ability to act as a DisposableVM Template with:
qvm-prefs <vmname> template_for_dispvms True
The default system wide DisposableVM Template can be changed with qubes-prefs default_dispvm.
By combining the two, choosing Open in DisposableVM from inside an AppVM will open the document in a DisposableVM based on the default DisposableVM Template you specified.
You can change this behaviour for individual VMs: in the Application Menu, open Qube Settings for the VM in question and go to the "Advanced" tab. Here you can edit the "Default DisposableVM" setting to specify which DisposableVM Template will be used to launch DisposableVMs from that VM. This can also be changed from the command line with:
qvm-prefs <VM> default_dispvm <DISPOSABLEVM_TEMPLATE>
For example, anon-whonix has been set to use whonix-ws-dvm as its default_dispvm, instead of the system default.
You can even set an AppVM that has also been configured as a DisposableVM Template to use itself, so DisposableVMs launched from within the AppVM/DisposableVM Template would inherit the same settings.
NetVM and firewall rules for DisposableVM Templates can be set as they can for a normal VM. By default a DisposableVM will inherit the NetVM and firewall settings of the DisposableVM Template on which it is based. This is a change in behaviour from R3.2, where DisposableVMs would inherit the settings of the AppVM from which they were launched. Therefore, launching a DisposableVM from an AppVM will result in it using the network/firewall settings of the DisposableVM Template on which it is based. For example, if an AppVM uses sys-net as its NetVM, but the default system DisposableVM uses sys-whonix, any DisposableVM launched from this AppVM will have sys-whonix as its NetVM.
Warning: The opposite is also true.
This means if you have changed anon-whonix's default_dispvm to use the system default, and the system default DisposableVM uses sys-net, launching a DisposableVM from inside anon-whonix will result in the DisposableVM using sys-net.
A DisposableVM launched from the Start Menu inherits the NetVM and firewall settings of the DisposableVM Template on which it is based. Note that changing the "NetVM" setting for the system default DisposableVM Template does affect the NetVM of DisposableVMs launched from the Start Menu. Different DisposableVM Templates with individual NetVM settings can be added to the Start Menu.
Important Notes: Some DisposableVM Templates will automatically create a menu item to launch a DVM, if you do not see an entry and want to add one please use the command:
qvm-features deb-dvm appmenus-dispvm 1
To launch a DisposableVM Template from the command line, in dom0 please type the following:
qvm-run --dispvm=<DISPOSABLEVM_TEMPLATE> --service qubes.StartApp+NameOfApp
Opening a file in a DisposableVM via GUI
In an AppVM's file manager, right click on the file you wish to open in a DisposableVM, then choose "Open in DisposableVM". Wait a few seconds and the default application for this file type should appear displaying the file content. This app is running in its own dedicated VM -- a DisposableVM created for the purpose of viewing or editing this very file. Once you close the viewing application the whole DisposableVM will be destroyed. If you have edited the file and saved the changes, the changed file will be saved back to the original AppVM, overwriting the original.
Opening a fresh web browser instance in a new DisposableVM
Sometimes it is desirable to open an instance of Firefox within a new fresh DisposableVM. This can be done easily using the Start Menu: just go to Application Menu -> DisposableVM -> DisposableVM:Firefox web browser. Wait a few seconds until a web browser starts. Once you close the viewing application the whole DisposableVM will be destroyed.
Opening a file in a DisposableVM via command line (from AppVM)
Use the qvm-open-in-dvm command from a terminal in your AppVM:
[user@work-pub ~]$ qvm-open-in-dvm Downloads/apple-sandbox.pdf
Note that the qvm-open-in-dvm process will not exit until you close the application in the DisposableVM.
Starting an arbitrary program in a DisposableVM from an AppVM
Sometimes it can be useful to start an arbitrary program in a DisposableVM. The DisposableVM will stay running so long as the process which started the DisposableVM has not exited. Some applications, such as GNOME Terminal, do not wait for the application to close before the process exits (details here). Starting an arbitrary program can be done from an AppVM by running
[user@vault ~]$ qvm-run '@dispvm' xterm
The created DisposableVM can be accessed via other tools (such as qvm-copy-to-vm) using its disp#### name as shown in the Qubes Manager or qvm-ls.
Starting an arbitrary application in a DisposableVM via command line from dom0
The Application Launcher has shortcuts for opening a terminal and a web browser in dedicated DisposableVMs, since these are very common tasks. The DisposableVM will stay running so long as the process which started the DisposableVM has not exited. Some applications, such as GNOME Terminal, do not wait for the application to close before the process exits (details here). It is possible to start an arbitrary application in a DisposableVM directly from dom0 by running:
$ qvm-run --dispvm=<DISPOSABLEVM_TEMPLATE> --service qubes.StartApp+xterm
The label color will be inherited from <DISPOSABLEVM_TEMPLATE>.
(The DisposableVM Application Launcher shortcut used for starting programs runs a very similar command to the one above.)
Opening a link in a DisposableVM based on a non-default DisposableVM Template from a qube
Suppose that the default DisposableVM Template for your email qube has no networking (e.g., so that untrusted attachments can't phone home).
However, sometimes you want to open email links in DisposableVMs.
Obviously, you can't use the default DisposableVM Template, since it has no networking, so you need to be able to specify a different DisposableVM Template.
You can do that with this command from the email qube (as long as your RPC policies allow it):
$ qvm-open-in-vm @dispvm:<ONLINE_DISPOSABLEVM_TEMPLATE> https://www.qubes-os.org
This will create a new DisposableVM based on <ONLINE_DISPOSABLEVM_TEMPLATE>, open the default web browser in that DisposableVM, and navigate to https://www.qubes-os.org.
Example of RPC policies to allow this behavior
In dom0, add the following line at the beginning of the file /etc/qubes-rpc/policy/qubes.OpenURL
@anyvm @dispvm:<ONLINE_DISPOSABLEVM_TEMPLATE> allow
This line means:
- FROM: Any VM
- TO: A DisposableVM based on
<ONLINE_DISPOSABLEVM_TEMPLATE> - WHAT: Allow sending an "Open URL" request
In other words, any VM will be allowed to create a new DisposableVM based on <ONLINE_DISPOSABLEVM_TEMPLATE> and open a URL inside of that DisposableVM.
More information about RPC policies for DisposableVMs can be found here.
Customizing DisposableVMs
You can change the template used to generate the DisposableVMs, and change settings used in the DisposableVM savefile. These changes will be reflected in every new DisposableVM based on that template. Full instructions can be found here.