qubes-doc/user/advanced-topics/how-to-install-software-in-dom0.md

---
lang: en
layout: doc
permalink: /doc/how-to-install-software-in-dom0/
redirect_from:
- /doc/software-update-dom0/
- /en/doc/software-update-dom0/
- /doc/SoftwareUpdateDom0/
- /wiki/SoftwareUpdateDom0/
ref: 194
title: How to Install Software in Dom0
---

**Warning:** Installing software in dom0 is for advanced users only. Doing so
has the potential to compromise your entire Qubes OS installation. Exercise
extreme caution.

## 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 template distro's updates, and this would be far
too costly for us to maintain.

## How to update dom0

See [How to Update](/doc/how-to-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](/doc/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](/doc/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:

- `kernel`: an older LTS kernel that has passed Qubes [testing](/doc/testing/)
  (the default dom0 kernel)
- `kernel-latest`: the latest release from kernel.org that has passed Qubes
  [testing](/doc/testing/) (useful for [troubleshooting newer
  hardware](/doc/newer-hardware-troubleshooting/))

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](/doc/managing-vm-kernels/) 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](https://groups.google.com/d/msg/qubes-users/m8sWoyV58_E/HYdReRIYBAAJ).

## 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](/doc/privacy/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
```