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
Fedora CoreOS Config (FCC) and adapt the contents for
FCOS. Since many of the configuration details have changed, you should
reference this page and the
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.
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
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 FCC files, 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.
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 FCC configuration for details about writing directories and files to FCOS.
FCCs no longer have a separate section for network configuration. Use the FCC
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, the data is collected (without unique identifiers) by
To prevent any information from being collected or transmitted by the pinger, you can disable reporting. To do so, drop a config snippet into
/etc/fedora-coreos-pinger/config.d/99-disable-reporting.tomlcontaining the following:
[reporting] enabled = false
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.