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Additional packages

The controller domain (dom0) is a privileged Linux VM, based on CentOS.

It may be useful to add more packages to it, with precaution. The XCP-ng project offers some in its repositories, and other packages can be installed from CentOS, EPEL, or even third party repositories.


Best effort support is provided for additional packages provided by the XCP-ng project (supported list for XCP-ng 8.2). No support is provided for other additional packages, even if installed from our repositories, as they contain build dependencies not supposed to be installed in production.

📜 Rules

1. Never enable additional repositories

The update process for XCP-ng assumes that only XCP-ng repositories are enabled. If you enable more repositories, updates may get pulled from there and overwrite XCP-ng packages and thus break your system.

Warning: some third party repositories are auto-enabled when installed. This is the case of EPEL, for example. Installing epel-release (the common way to enable it on CentOS) will automatically enable it. To avoid this, EPEL repositories are already added at system installation on XCP-ng, but they are disabled.

But then, how to install from such additional repositories?

You simply need to learn yum's --enablerepo switch. Very handy, it enables one or more repositories only for the current execution of the command, without enabling the repo system-wide.

See section How to install below for practical details.

To disable a repository, edit /etc/yum.repos.d/name_of_repo.repo and set enabled=0 where the value is 1.

2. Prefer additional packages from XCP-ng's own repositories

We offer a number of additional packages ranging from ZFS support, newer drivers or newer kernel, to small utilities such as vim, joe, iperf, mc, etc.).

A regularly updated list of such utilities for XCP-ng 8.2 is available at

The packages from this list are supported on a best-effort basis.

The repositories are already enabled by default. Install with yum install name_of_package. For example: yum install zfs.

In some cases, packages may be listed in the above list but not available yet in the default repositories. This means they are still undergoing tests and reside in the xcp-ng-testing repository. If you want to test them, add --enablerepo=xcp-ng-testing to the installation command.


Anything installed outside this list of packages is at your own risk, even if that comes from XCP-ng repositories.

3. Do not overwrite existing packages from the system

Some third party repositories - including CentOS repositories and EPEL - contain packages that have a higher version number than ours. yum will tend to want to install them over our packages. Always check that it is not trying to overwrite one of our installed packages.

4. Keep your dom0 minimal

The controller domain is not an all-purpose Linux system. It must remain minimal to do what it is meant to do efficiently, and also to ensure that every component installed receives relevant security fixes.

  • Avoid bloat (do not attempt to transform it into a Linux workstation. Use a VM instead.)
  • Avoid CPU or RAM-intensive programs
  • Avoid software that pulls in many dependencies
  • Avoid any software that may interfere with the existing
  • Avoid software that widens the attack surface on your hosts

5. Known Security Risks


If you are using encrypted tunnels using openvswitch-ipsec and libreswan, for example through Xen Orchestra's SDN Controller there are security advisories you need to know about, there are 2 CVEs that are affecting our current libreswan version:

  • CVE-2023-38712: Invalid IKEv1 repeat IKE SA delete causes crash and libreswan to restart
  • CVE-2023-38710: Invalid IKEv2 REKEY proposal causes libreswan to restart

Patches for these are not really backportable, we therefore kept it as is and target updating packages in the next major release.

You can find information about all Libreswan CVEs on their security page.

Resulting security issue

The pluto daemon may be crashed by malformed IKE (both v1 and v2) delete/notify requests, resulting in a DoS on the keying service. If the daemon is restarted in loop quickly enough, this could as well lead to a DoS of the whole host.

Vulnerability Perimeter

Various point regarding how critical this is:

  • these packages are not installed by default, and only required for encrypted tunnels
  • no privilege escalation
  • pluto will only process these packets if they are coming from an authenticated peer, limiting the possible sources

6. Ask before

If you have pro support, ask there. As part of the support, additional supported packages - such as new drivers - may be provided. Else ask the community on the forum.

🦮 How to install

Before doing any change, start keeping track somewhere of any change you bring to the system. This will help for:

  • support
  • knowing what packages you need to update regularly for security fixes or bugfixes
  • reinstalling them after a system upgrade via the installation ISO

From XCP-ng repositories

yum install name_of_package

From CentOS repositories

The CentOS repos are already installed but are disabled, on purpose. Install from them with:

yum install name_of_package --enablerepo=base,updates

Make sure it will not try to overwrite system packages with updates from CentOS. XCP-ng uses fixed or modified versions of some CentOS packages whereas the CentOS repos point at the latest.

From EPEL repositories

On XCP-ng, the EPEL repos are already installed but are disabled, on purpose. Install from them with:

yum install name_of_package --enablerepo=epel

Sometimes you'll need extra dependencies from CentOS. Replace the command with:

yum install name_of_package --enablerepo=epel,base,updates

And as above make sure no package from the system will get overwritten in the process.

From other third party repositories

  1. Avoid that if possible
  2. Be extra cautious
  3. After installing the repository, disable it right away (enabled=0 in repo file)
  4. install packages with: yum install name_of_package --enablerepo=name_of_repo

And as usual make sure it won't overwrite existing packages...

📦 Up to date additional packages

If you installed from XCP-ng repositories, they will be updated like the rest of the XCP-ng system.

If you installed from any other repository, including CentOS and EPEL, you need to update them (and their dependencies) manually

♻️ System upgrade

See upgrade section for a discussion of the differences between "Installer upgrade" and "yum-style upgrade".

Installer upgrade will reinstall the system from scratch and just keep your configuration related to XCP-ng (network, VMs, SRs, etc.). Anything else will have to be re-done.

yum-style upgrade will try to update or keep the packages that you installed. Packages installed from XCP-ng repositories should get updated seamlessly. Packages from other repositories will not get updated: they may be left in place (then you'll have to update them yourselves if needed), removed (due to package conflicts or because they are obsoleted by packages from the updated XCP-ng) or even make the upgrade fail until they are manually removed.