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qubes-doc/user/common-tasks/software-update-dom0.md

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194 Installing and updating software in dom0

Installing and updating software in dom0

Updating dom0 is one of the main steps in Updating Qubes OS. It is very important to keep dom0 up-to-date with the latest security updates. We also publish dom0 updates for various non-security bug fixes and enhancements to Qubes components. In addition, you may wish to update the kernel, drivers, or libraries in dom0 when troubleshooting newer hardware.

Security

Since there is no networking in dom0, any bugs discovered in dom0 desktop components (e.g., the window manager) are unlikely to pose a problem for Qubes, since none of the third-party software running in dom0 is accessible from VMs or the network in any way. Nonetheless, since software running in dom0 can potentially exercise full control over the system, it is important to install only trusted software in dom0.

The install/update process is split into two phases: resolve and download and verify and install. The resolve and download phase is handled by the UpdateVM. (The role of UpdateVM can be assigned to any VM in the Qube Manager, and there are no significant security implications in this choice. By default, this role is assigned to the FirewallVM.) After the UpdateVM has successfully downloaded new packages, they are sent to dom0, where they are verified and installed. This separation of duties significantly reduces the attack surface, since all of the network and metadata processing code is removed from the TCB.

Although this update scheme is far more secure than directly downloading updates in dom0, it is not invulnerable. For example, there is nothing that the Qubes OS Project can feasibly do to prevent a malicious RPM from exploiting a hypothetical bug in the cryptographic signature verification operation. At best, we could switch to a different distro or package manager, but any of them could be vulnerable to the same (or a similar) attack. While we could, in theory, write a custom solution, it would only be effective if Qubes repos included all of the regular TemplateVM distro's updates, and this would be far too costly for us to maintain.

How to update dom0

In the Qube Manager, simply select dom0 in the VM list, then click the Update VM system button (the blue, downward-pointing arrow). In addition, updating dom0 has been made more convenient: You will be prompted on the desktop whenever new dom0 updates are available and given the choice to run the update with a single click.

Alternatively, command-line tools are available for accomplishing various update-related tasks (some of which are not available via Qubes VM Manager). In order to update dom0 from the command line, start a console in dom0 and then run one of the following commands:

To check and install updates for dom0 software:

$ sudo qubes-dom0-update

How to install a specific package

To install additional packages in dom0 (usually not recommended):

$ sudo qubes-dom0-update anti-evil-maid

You may also pass the --enablerepo= option in order to enable optional repositories (see yum configuration in dom0). However, this is only for advanced users who really understand what they are doing. You can also pass commands to dnf using --action=....

How to downgrade a specific package

WARNING: Downgrading a package can expose your system to security vulnerabilities.

  1. Download an older version of the package:

    sudo qubes-dom0-update package-version

    Dnf will say that there is no update, but the package will nonetheless be downloaded to dom0.

  2. Downgrade the package:

    sudo dnf downgrade package-version

How to re-install a package

You can re-install in a similar fashion to downgrading.

  1. Download the package:

    sudo qubes-dom0-update package

    Dnf will say that there is no update, but the package will nonetheless be downloaded to dom0.

  2. Re-install the package:

    sudo dnf reinstall package

    Note that dnf will only re-install if the installed and downloaded versions match. You can ensure they match by either updating the package to the latest version, or specifying the package version in the first step using the form package-version.

How to uninstall a package

If you've installed a package such as anti-evil-maid, you can remove it with the following command:

sudo dnf remove anti-evil-maid

Testing repositories

There are three Qubes dom0 testing repositories:

  • qubes-dom0-current-testing -- testing packages that will eventually land in the stable (current) repository
  • qubes-dom0-security-testing -- a subset of qubes-dom0-current-testing that contains packages that qualify as security fixes
  • qubes-dom0-unstable -- packages that are not intended to land in the stable (qubes-dom0-current) repository; mostly experimental debugging packages

To temporarily enable any of these repos, use the --enablerepo=<repo-name> option. Example commands:

sudo qubes-dom0-update --enablerepo=qubes-dom0-current-testing
sudo qubes-dom0-update --enablerepo=qubes-dom0-security-testing
sudo qubes-dom0-update --enablerepo=qubes-dom0-unstable

To enable or disable any of these repos permanently, change the corresponding enabled value to 1 in /etc/yum.repos.d/qubes-dom0.repo.

Contributed package repository

Please see installing contributed packages.

Kernel upgrade

This section describes upgrading the kernel in dom0 and domUs.

dom0

The packages kernel and kernel-latest are for dom0.

In the current repository:

In the current-testing repository:

  • kernel: the latest LTS kernel from kernel.org at the time it was built.
  • kernel-latest: the latest release from kernel.org at the time it was built.

domU

The packages kernel-qubes-vm and kernel-latest-qubes-vm are for domUs. See Managing VM kernel for more information.

Example

(Note that the following example enables the unstable repo.)

sudo qubes-dom0-update --enablerepo=qubes-dom0-unstable kernel kernel-qubes-vm

If the update process does not automatically do it (you should see it mentioned in the CLI output from the update command), you may need to manually rebuild the EFI or grub config depending on which your system uses.

EFI: Replace the example version numbers with the one you are upgrading to.

sudo dracut -f /boot/efi/EFI/qubes/initramfs-4.14.35-1.pvops.qubes.x86_64.img 4.14.35-1.pvops.qubes.x86_64

Grub2

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Reboot required.

If you wish to upgrade to a kernel that is not available from the repos, then there is no easy way to do so, but it may still be possible if you're willing to do a lot of work yourself.

Changing default kernel

This section describes changing the default kernel in dom0. It is sometimes needed if you have upgraded to a newer kernel and are having problems booting, for example. The procedure varies depending on if you are booting with UEFI or grub. On the next kernel update, the default will revert to the newest.

EFI

sudo nano /boot/efi/EFI/qubes/xen.cfg

In the [global] section at the top, change the default= line to match one of the three boot entries listed below. For example,

default=4.19.67-1.pvops.qubes.x86_64

Grub2

sudo nano /etc/default/grub
[update the following two lines, add if needed]
GRUB_DISABLE_SUBMENU=false
GRUB_SAVEDEFAULT=true
[save and exit nano]
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Then, reboot. Once the grub menu appears, choose "Advanced Options for Qubes (with Xen hypervisor)". Next, the top menu item (for example, "Xen hypervisor, version 4.8.5-9.fc25"). Select the kernel you want as default, and it will be remembered for next boot.

Updating over Tor

Requires installed Whonix.

Go to Qubes VM Manager -> System -> Global Settings. See the UpdateVM setting. Choose your desired Whonix-Gateway ProxyVM from the list. For example: sys-whonix.

Qubes VM Manager -> System -> Global Settings -> UpdateVM -> sys-whonix