Migrating from CoreOS Container Linux (CL) to Fedora CoreOS (FCOS)
Fedora CoreOS is the official successor of CoreOS Container Linux, which reached its end of life on May 26, 2020. This page attempts to document the differences between CL and FCOS to ease the transition to FCOS.
To migrate from CL to FCOS, you must convert your old Container Linux Configs, Ignition configs, or
cloud-config files to a Butane config and adapt the contents for FCOS. Since many of the configuration details have changed, you should reference this page and the CL migration issue on GitHub.
The following changes have been made to the installation process:
coreos-installscript has been replaced with
coreos-installer. It offers similar functionality.
coreos.autologinkernel command-line parameter is not currently supported in FCOS. For access recovery purposes, there are instructions available here.
Certain CL platforms, such as Vagrant, are not yet supported in FCOS. Refer to the Download page to see the available image types.
Software package changes
etcdis not included in FCOS. Refer to Running etcd for instructions to run it as a container on FCOS.
flannelis not included in FCOS.
The Podman container runtime is included in FCOS and is the recommended container runtime. The rkt container runtime is not included.
FCOS does not have a recommended mechanism to select the version of
Network configuration is now handled by NetworkManager instead of
For time synchronization, use
Automatic updates are now coordinated by Zincati, as described in the Zincati documentation. The rollback mechanism (via grub) is now provided by
The functionality of the reboot manager (
locksmith) is rolled into Zincati.
update-ssh-keystool is not provided on FCOS. sshd uses a helper program to read key files directly out of
When writing Butane configs, note the following changes:
coreos-metadatais now Afterburn. The prefix of the metadata variable names has changed from
AFTERBURN_, and the following platform names have changed:
For more info, see the Afterburn documentation.
By default, FCOS does not allow password logins via SSH. We recommend configuring SSH keys instead. If needed, you can enable SSH password authentication.
usermodis not yet fully-functional on FCOS, there is a
dockergroup in the
/etc/groupfile. This is a stop-gap measure to facilitate a smooth transition to FCOS. The team is working on a more functional
usermod, at which time the
dockergroup will no longer be included by default. See the docker group issue.
There is no way to create directories below the
/directory. Changes are restricted to
/var. Refer to the documentation for the
storagenode of the Butane config for details about writing directories and files to FCOS.
Butane configs no longer have a separate section for network configuration. Use the Butane
filessection to write a NetworkManager key file instead.
FCOS provides best-effort stability, and may occasionally include regressions or breaking changes for some use cases or workloads.
CL had three release channels:
stable. The FCOS production release streams are
stable, with somewhat different semantics.
In general, SELinux confinement should work the same as in Fedora.
To deploy an Ignition config as part of a PXE image (a "custom OEM" in CL terminology), follow the same process as in CL, but place the
config.ignfile in the root of the archive.
In CL, metrics/telemetry data was collected by the update mechanism. In FCOS, nodes are counted (without unique identifiers) via the Count Me mechanism.
Cloud CLI clients are not included in FCOS. There is an initiative to create a "tools" container to run on FCOS.
When opening an existing file in a sticky directory, the behavior differs from CL. See the relevant systemd commit.
CL left Simultaneous Multi-Threading (SMT) enabled but advised users to turn it off if their systems were vulnerable to certain issues such as L1TF or MDS. By default, FCOS automatically disables SMT for vulnerable systems.
dockeruses the default configuration from Fedora, which is different under many aspects. Notably the logging driver is set to
journaldand live-restore is enabled.
The default filesystem on CL was
ext4. On FCOS, the default is
While CL used systemd socket activation for
sshd, FCOS starts
sshdat startup by default.
CL had an "OEM partition" at
/usr/share/oemwith a user-customizable GRUB config and some additional tools, but FCOS does not have this.
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