Disposable VM Customization

Qubes 4.0

Disposable VM (DispVM) in Qubes 4.0 can be based on any TemplateBasedVM. You can also choose to use different AppVMs for different Disposable VMs. To prepare AppVM to be a base for Disposable VM, you need to set template_for_dispvms property, for example:

[user@dom0 ~]$ qvm-prefs fedora-26-dvm template_for_dispvms True

Additionally, if you want to have menu entries for starting applications in Disposable VM based on this AppVM (instead of in the AppVM itself), you can achieve it with appmenus-dispvm feature:

[user@dom0 ~]$ qvm-features fedora-26-dvm appmenus-dispvm 1

Creating new Disposable VM base AppVM

In Qubes 4.0, you’re no longer restricted to a single DVM Template. Instead, you can create as many as you want. Whenever you start a new Disposable VM, you can choose to base it on whichever DVM Template you like. To create new DVM Template, lets say custom-dvm, based on debian-9 template, use following commands:

[user@dom0 ~]$ qvm-create --template debian-9 --label red custom-dvm
[user@dom0 ~]$ qvm-prefs custom-dvm template_for_dispvms True
[user@dom0 ~]$ qvm-features custom-dvm appmenus-dispvm 1

Additionally you may want to set it as default DVM Template:

[user@dom0 ~]$ qubes-prefs default_dispvm custom-dvm

The above default is used whenever a qube request starting a new Disposable VM and do not specify which one (for example qvm-open-in-dvm tool). This can be also set in qube settings and will affect service calls from that qube. See qrexec documentation for details.

If you wish to use the fedora-minimal template as a DVM Template, see the “DVM Template” use case under fedora-minimal customization.

Customization of Disposable VM

It is possible to change the settings for each new Disposable VM (DispVM). This can be done by customizing the base AppVM:

  1. Start a terminal in the fedora-26-dvm qube (or another base for DispVM) by running the following command in a dom0 terminal. (If you enable appmenus-dispvm feature (as explained at the top), applications menu for this VM (fedora-26-dvm) will be “Disposable: fedora-26-dvm” (instead of “Domain: fedora-26-dvm”) and entries there will start new DispVM based on that VM (fedora-26-dvm). Not in that VM (fedora-26-dvm) itself).

    [user@dom0 ~]$ qvm-run -a fedora-26-dvm gnome-terminal
    
  2. Change the qube’s settings and/or applications, as desired. Some examples of changes you may want to make include:
    • Changing Firefox’s default startup settings and homepage.
    • Changing default editor, image viewer.
    • Changing the DispVM’s default NetVM. For example, you may wish to set the NetVM to “none.” Then, whenever you start a new DispVM, you can choose your desired ProxyVM manually (by changing the newly-started DispVMs settings). This is useful if you sometimes wish to use a DispVM with a Whonix Gateway, for example. It is also useful if you sometimes wish to open untrusted files in a network-disconnected DispVM.
  3. Shutdown the qube (either by poweroff from qube’s terminal, or qvm-shutdown from dom0 terminal).

Using static Disposable VMs for sys-*

You can use a static DispVM for sys-* as long as it is stateless. For example, a sys-net using DHCP or sys-usb will work. In most cases sys-firewall will also work, even if you have configured AppVM firewall rules. The only exception is if you require something like VM to VM communication and have manually edited iptables or other items directly inside the firewall AppVM.

To create one that has no PCI devices attached, such as for sys-firewall:

qvm-create -C DispVM -l red <sys-VMName>
qvm-prefs <sys-VMName> autostart true
qvm-prefs <sys-VMName> netvm <sys-net>
qvm-prefs <sys-VMName> provides_network true

Next, set the old sys-firewall autostart to false, and update any references to the old one to instead point to the new. For example, with qvm-prefs work netvm sys-firewall2.

To create one with a PCI device attached such as for sys-net or sys-usb, use the additional commands as follows.

Note You can use qvm-pci to determine the <BDF>. Also, you will often need to include the -o no-strict-reset=True option with USB controllers.

qvm-create -C DispVM -l red <sys-VMName>
qvm-prefs <sys-VMName> virt_mode hvm
qvm-service <sys-VMName> meminfo-writer off
qvm-pci attach --persistent <sys-VMName> dom0:<BDF>
qvm-prefs <sys-VMName> autostart true
qvm-prefs <sys-VMName> netvm ''
# optional, if this DispVM will be providing networking
qvm-prefs <sys-VMName> provides_network true

Next, set the old sys- VM’s autostart to false, and update any references to the old one. For example, qvm-prefs sys-firewall netvm <sys-VMName>. See below for a complete example of a sys-net replacement:

qvm-create -C DispVM -l red sys-net2
qvm-prefs sys-net2 virt_mode hvm
qvm-service sys-net2 meminfo-writer off
qvm-pci attach --persistent sys-net2 dom0:00_1a.0
qvm-prefs sys-net2 autostart true
qvm-prefs sys-net2 netvm ''
qvm-prefs sys-net2 provides_network true
qvm-prefs sys-net autostart false
qvm-prefs sys-firewall netvm sys-net2
qubes-prefs clockvm sys-net2

Note that these types of DispVMs will not show in the Application menu, but you can still get to a terminal if needed with qvm-run <sys-VMName> gnome-terminal.

Adding programs to Disposable VM Application Menu

For added convenience, arbitrary programs can be added to the Application Menu of the Disposable VM.

In order to do that, select “Qube settings” entry in selected base AppVM, go to “Applications” tab and select desired applications as for any other qube.

Note that currently only applications whose main process keeps running until you close the application (i.e. do not start a background process instead) will work. One of known examples of incompatible applications is GNOME Terminal (shown on the list as “Terminal”). Choose different terminal emulator (like XTerm) instead.

Deleting Disposable VM

Deleting disposable VM is slightly peculiar. While working in a VM or disposable VM, you may want to open a document in another disposable VM. For this reason, the property default_dispvm may be set to the name of your disposable VM in a number of VMs:

[user@dom0 ~]$ qvm-prefs workvm | grep default_disp
default_dispvm        -  custom-dvm

This will prevent the deletion of the DVM. In order to fix this you need to unset the default_disp property:

[user@dom0 ~]$ qvm-prefs workvm default_disp ""

You can then delete the DVM:

[user@dom0 ~]$ qvm-remove custom-dvm
This will completely remove the selected VM(s)
  custom-dvm

If you still encounter the issue, you may have forgot to clean an entry. Looking at the system logs will help you

[user@dom0 ~]$ journalctl | tail

Qubes 3.2

Changing the DVM Template

You may want to use a non-default template the DVM Template. One example is to use a less-trusted template with some less trusted, third-party, often unsigned, applications installed, such as e.g. third-party printer drivers.

In order to regenerate the Disposable VM “snapshot” (called ‘savefile’ on Qubes) one can use the following command in Dom0:

[user@dom0 ~]$ qvm-create-default-dvm <custom-template-name>

This would create a new Disposable VM savefile based on the custom template. For example <custom-template-name> could be the name of the existing debian-8 vm, which creates the disposable vm debain-8-dvm. Now, whenever one opens a file (from any AppVM) in a Disposable VM, a Disposable VM based on this template will be used.

One can easily verify if the new Disposable VM template is indeed based on a custom template (in the example below the template called “f17-yellow” was used as a basis for the Disposable VM):

[user@dom0 ~]$ ll /var/lib/qubes/dvmdata/
total 0
lrwxrwxrwx 1 user user 45 Mar 11 13:59 default_dvm.conf -> /var/lib/qubes/appvms/f17-yellow-dvm/dvm.conf
lrwxrwxrwx 1 user user 49 Mar 11 13:59 default_savefile -> /var/lib/qubes/appvms/f17-yellow-dvm/dvm-savefile
lrwxrwxrwx 1 user user 47 Mar 11 13:59 savefile_root -> /var/lib/qubes/vm-templates/f17-yellow/root.img

If you wish to use the fedora-minimal template as a DVM Template, see the “DVM Template” use case under fedora-minimal customization.

Customization of Disposable VM

It is possible to change the settings of each new Disposable VM (DispVM). This can be done by customizing the DispVM template:

  1. Start a terminal in the fedora-23-dvm TemplateVM by running the following command in a dom0 terminal. (By default, this TemplateVM is not shown in Qubes VM Manager. However, it can be shown by selecting “Show/Hide internal VMs.”)

    [user@dom0 ~]$ qvm-run -a fedora-23-dvm gnome-terminal
    
  2. Change the VM’s settings and/or applications, as desired. Note that currently Qubes supports exactly one DispVM template, so any changes you make here will affect all DispVMs. Some examples of changes you may want to make include:
    • Changing Firefox’s default startup settings and homepage.
    • Changing Nautilus’ default file preview settings.
    • Changing the DispVM’s default NetVM. For example, you may wish to set the NetVM to “none.” Then, whenever you start a new DispVM, you can choose your desired ProxyVM manually (by changing the newly-started DispVM’s settings). This is useful if you sometimes wish to use a DispVM with a Whonix Gateway, for example. It is also useful if you sometimes wish to open untrusted files in a network-disconnected DispVM.
  3. Create an empty /home/user/.qubes-dispvm-customized file in the VM (not in dom0):

    [user@fedora-23-dvm ~]$ touch /home/user/.qubes-dispvm-customized
    
  4. Shutdown the VM (either by poweroff from VM terminal, or qvm-shutdown from dom0 terminal).
  5. Regenerate the DispVM template using the default template:

    [user@dom0 ~]$ qvm-create-default-dvm --default-template
    

    Or, if you’re using a non-default template, regenerate the DispVM using your custom template:

    [user@dom0 ~]$ qvm-create-default-dvm <custom-template-name>
    

Note: All of the above requires at least qubes-core-vm >= 2.1.2 installed in template.

Adding arbitrary programs to Disposable VM Application Menu

For added convenience, arbitrary programs can be added to the Application Menu of the Disposable VM. In order to do that create (e.g.) arbitrary.desktop file in /usr/local/share/applications in Dom0. That file will point to the desired program. Use the following template for the file:

[Desktop Entry]
Version=1.0
Type=Application
Exec=sh -c 'echo arbitrary | /usr/lib/qubes/qfile-daemon-dvm qubes.VMShell dom0 DEFAULT red'
Icon=dispvm-red
Terminal=false
Name=DispVM: Arbitrary Name
GenericName=DispVM: Arbitrary Generic Name
StartupNotify=false
Categories=Network;X-Qubes-VM;

Next, the /etc/xdg/menus/applications-merged/qubes-dispvm.menu file has to be modified so that it points to the newly-created .desktop file. (If you use i3 you can skip this step; the shortcut gets added to dmenu automatically.)

Add a <Filename>arbitrary.desktop</Filename> line so that your modified file looks like this:

<Include>
<Filename>qubes-dispvm-firefox.desktop</Filename>
<Filename>qubes-dispvm-xterm.desktop</Filename>
<Filename>arbitrary.desktop</Filename>
</Include>

After saving the changes the new shortcut should appear in the Disposable VM Applications menu.