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Client administration

  1. Administering an rpm-ostree based system
    1. Hybrid image/packaging via package layering
    2. Modularity
    3. Rebasing
    4. Other local state changes
    5. Experimental interface
  2. Using overrides and usroverlay
    1. Resetting overrides
    2. Applying overrides live
    3. Using usroverlay
    4. Removing a base package
  3. Filesystem layout
  4. Operating system changes

Administering an rpm-ostree based system

At the moment, there are four primary commands to be familiar with on an rpm-ostree based system.

# rpm-ostree status

Will show you your deployments in the order in which they will appear in the bootloader, the first deployment in the list being the current default one. The shows the currently booted deployment.

# rpm-ostree upgrade

Will prepare a system upgrade offline, creating a new deployment (root filesystem) and set it as the default for the next boot. The update will be “finalized” at shutdown and a new bootloader entry prepared. Hence, use reboot to apply the update.

# rpm-ostree rollback

This rolls back to the previous state, i.e. the default deployment changes places with the non-default one. By default, the rpm-ostree upgrade will keep at most two bootable “deployments”, though the underlying technology supports more.

# rpm-ostree deploy <version>

This command makes use of the server-side history feature of OSTree. It will search the history of the current branch for a commit with the specified version, and deploy it. This can be used in scripts to ensure consistent updates. For example, if the upstream OS vendor provides an update online, you might not want to deploy it until you’ve tested it. This helps ensure that when you upgrade, you are getting exactly what you asked for.

Hybrid image/packaging via package layering

It is possible to dynamically add more packages onto the system that are not part of the commit composed on the server. These additional “layered” packages are persistent across upgrades, rebases, and deploys (contrast with the ostree unlocking mechanism).

This is where the true hybrid image/package nature of rpm-ostree comes into play; you get a combination of the benefits of images and packages. The package updates are still fully transactional and offline.

For example, you can use package layering to install 3rd party kernel modules, or userspace driver daemons such as pcsc-lite-ccid. While most software should go into a container, you have full flexibilty to use packages where it suits.

# rpm-ostree install <pkg>

Will download the target package, its dependencies, and create a new deployment with those packages installed. It is also possible to specify a local package which is not part of a repository.

To remove layered packages, use:

# rpm-ostree uninstall <pkg>

By default, every rpm-ostree operation is “offline” - it has no effect on your running system, and will only take effect when you reboot. This “pending” state is called the “pending deployment”. Operations can be chained; for example, if you invoke rpm-ostree upgrade after installing a package, your new root will upgraded with the package also installed.

As a special case, it is supported to live-apply just package additions, assuming that there are not other pending changes:

# rpm-ostree install -yA <pkg>

Modularity

rpm-ostree provides experimental support for modules, a way for the distribution to ship multiple versions (or “streams”) of the same software.

A module can have multiple streams, and each stream can have multiple profiles. A profile is a set of packages for common use cases (e.g. you can have a “client” and “server” profile, each installing different packages).

rpm-ostree ex module enable enables a module stream and allow you to individually pick packages to rpm-ostree install from that stream. rpm-ostree ex module install installs module stream profiles directly.

For example, to enable the cri-o:1.20 module stream, use:

# rpm-ostree ex module enable cri-o:1.20

You can then rpm-ostree install individual packages from the enabled module.

Or to install a predefined profile, use e.g.:

# rpm-ostree ex module install cri-o:1.20/default

For more information about modularity, see the Fedora documentation. In particular, this page provides sample syntax invocations.

Rebasing

# rpm-ostree rebase -b $branchname

Your operating system vendor may provide multiple base branches. For example, Fedora Atomic Host has branches of the form:

  • fedora/27/aarch64/atomic-host
  • fedora/27/aarch64/testing/atomic-host
  • fedora/27/aarch64/updates/atomic-host
  • fedora/27/ppc64le/atomic-host
  • fedora/27/ppc64le/testing/atomic-host
  • fedora/27/ppc64le/updates/atomic-host
  • fedora/27/x86_64/atomic-host
  • fedora/27/x86_64/testing/atomic-host
  • fedora/27/x86_64/updates/atomic-host

You can use the rebase command to switch between these; this can represent a major version upgrade, or logically switching between different “testing” streams within the same release. Like every other rpm-ostree operation, All layered packages and local state will be carried across.

Other local state changes

See man rpm-ostree for more. For example, there is an rpm-ostree initramfs command that enables local initramfs generation.

Experimental interface

There is a generic rpm-ostree ex command that offers experimental features.

See man rpm-ostree for more information.

Using overrides and usroverlay

While some people talk about “immutability” when referring to image-based systems like rpm-ostree, in fact a top level goal of rpm-ostree is to empower users and system administrators. When something goes wrong, you are root on your own computer and should have the ability to apply overrides locally.

First, there is the rpm-ostree override replace command, which will replace an RPM, and apply that change persistently for the next boot - this is symmetric with how rpm-ostree install works.

For example, suppose you want to test a fix to podman. You can pass both direct HTTP URLs as well as local files:

$ rpm-ostree override replace https://kojipkgs.fedoraproject.org//packages/podman/3.3.1/1.fc34/x86_64/podman-3.3.1-1.fc34.x86_64.rpm

Another example with the kernel package; note you need to override exactly the set of installed packages:

$ ls -al kernel*.rpm
-rw-r--r--. 1 root root  8085596 Jan 27 22:02 kernel-4.18.0-123.el8.x86_64.rpm
-rw-r--r--. 1 root root 40709632 Jan 27 22:02 kernel-core-4.18.0-123.el8.x86_64.rpm
-rw-r--r--. 1 root root 32533504 Jan 27 22:02 kernel-modules-4.18.0-123.el8.x86_64.rpm
-rw-r--r--. 1 root root  8790996 Jan 27 22:02 kernel-modules-extra-4.18.0-123.el8.x86_64.rpm
$ rpm-ostree override replace ./kernel*.rpm

Resetting overrides

Use e.g. rpm-ostree override reset podman to undo the previous change. If invoked now, nothing will have happened to the booted filesystem tree.

Applying overrides live

Now, suppose that you want to test this change live. There are two choices. The first choice is to run the rpm-ostree override replace command above to stage the deployment, and then run

$ rpm-ostree apply-live --allow-replacement

This will pull the pending changes and apply them live. You can rpm-ostree apply-live --reset to revert back to the booted tree.

Using usroverlay

The second choice is rpm-ostree usroverlay which creates a transient writable overlayfs over /usr where you can do anything, such as e.g. copying in a podman binary generated on a build server somewhere that may not be in an RPM even.

The changes here will not persist across reboots, which makes this a great choice for testing.

One downside though is it does not currently work to rpm-ostree apply-live --reset today when rpm-ostree usroverlay is in place. It’s possible to find the original binaries in a previous deployment, or via ostree checkout of the base commit, etc.

Removing a base package

You can also just simply remove a base package with rpm-ostree override remove <pkg>. It will still be present in the underlying OSTree repository in /ostree/repo, but it will not be visible in the generated derived commit.

Similar to the override replace case, using rpm-ostree override reset will undo the change.

Filesystem layout

The only writable directories are /etc and /var. In particular, /usr has a read-only bind mount at all times. Any data in /var is never touched, and is shared across upgrades.

At upgrade time, the process takes the new default /etc, and adds your changes on top. This means that upgrades will receive new default files in /etc, which is quite a critical feature.

For more information, see OSTree: Adapting.

Operating system changes

  • The RPM database is stored in /usr/share/rpm, and is immutable.
  • A package nss-altfiles is required, and the system password database is stored in /usr/lib/passwd. Similar for the group database. This might change in the future; see this issue.