Fedora CoreOS ships with a simple default storage layout: the root partition is the last one and expands to take the full size of the disk. Apart from the boot partition, all data is stored on the root partition. See the Disk layout section for more details.
Below, we provide examples of various ways you can customize this.
Here’s an example FCC file to set up
/var on a separate partition on the same primary disk:
variant: fcos version: 1.2.0 storage: disks: - # The name of the primary block device. In virtio-based setups, this is # likely `/dev/vda`. Elsewhere, it's likely `/dev/sda`. device: /dev/vda # We do not want to wipe the partition table since this is the primary # device. wipe_table: false partitions: - size_mib: 0 # Start at 5G so that we leave enough space for the root partition. # See the important NOTE below about this. start_mib: 5000 # We assign a descriptive label to the partition. This is important # for referring to it in a device-agnostic way in other parts of the # configuration. label: var filesystems: - path: /var device: /dev/disk/by-partlabel/var # We can select the filesystem we'd like. format: ext4 # Ask FCCT to generate a mount unit for us so that this filesystem gets # mounted in the real root. with_mount_unit: true
You can of course mount only a subset of
/var into a separate partition. For example, to mount
variant: fcos version: 1.2.0 storage: disks: - device: /dev/vda wipe_table: false partitions: - size_mib: 0 # Start at 5G so that we leave enough space for the root partition. # See the important NOTE above about this. start_mib: 5000 label: containers filesystems: - path: /var/lib/containers device: /dev/disk/by-partlabel/containers format: xfs with_mount_unit: true
Alternatively, you can also mount storage from a separate disk. For example, here we mount
/var/log from a partition on
variant: fcos version: 1.2.0 storage: disks: - device: /dev/vdb wipe_table: false partitions: - size_mib: 0 start_mib: 0 label: log filesystems: - path: /var/log device: /dev/disk/by-partlabel/log format: xfs with_mount_unit: true
It is possible to reconfigure the root filesystem itself. You can use the path
/dev/disk/by-label/root to refer to the original root partition. You must ensure that the new filesystem also has a label of
|You must have at least 4G of RAM for root reprovisioning to work.|
Here’s an example of moving from xfs to ext4, but reusing the same partition on the primary disk:
variant: fcos version: 1.2.0 storage: filesystems: - device: /dev/disk/by-partlabel/root wipe_filesystem: true format: ext4 label: root
Similarly to the previous section, you can also move the root filesystem entirely. Here, we’re moving root to a RAID0 device:
variant: fcos version: 1.2.0 storage: raid: - name: myroot level: raid0 devices: - /dev/disk/by-id/virtio-disk1 - /dev/disk/by-id/virtio-disk2 filesystems: - device: /dev/md/myroot format: xfs wipe_filesystem: true label: root
You don’t need the
If you want to replicate the boot disk across multiple drives for resiliency to drive failure, you need to mirror all of the default partitions (root, boot, EFI System Partition, and bootloader code). There is special FCC syntax for this:
variant: fcos version: 1.3.0 boot_device: mirror: devices: - /dev/sda - /dev/sdb
Here is an example to configure a LUKS device at
variant: fcos version: 1.2.0 storage: luks: - name: data device: /dev/vdb filesystems: - path: /var/lib/data device: /dev/mapper/data format: xfs label: DATA with_mount_unit: true
The root filesystem can also be moved to LUKS. In the case of the root filesystem the LUKS device must be backed by clevis. There is simplified FCC syntax for encrypting the root filesystem; for example:
variant: fcos version: 1.3.0 boot_device: luks: tpm2: true
This is equivalent to the following expanded config:
variant: fcos version: 1.3.0 storage: luks: - name: root label: luks-root device: /dev/disk/by-partlabel/root clevis: tpm2: true wipe_volume: true filesystems: - device: /dev/mapper/root format: xfs wipe_filesystem: true label: root
The expanded config doesn’t include the
with_mount_unit keys; FCOS knows that the root partition is special and will figure out how to find it and mount it.
If you use Ignition to reconfigure or move the root partition, that partition is not automatically grown on first boot (see related discussions in this issue). In the case of moving the root partition to a new disk (or multiple disks), you should set the desired partition size using the
size_mib field. If reconfiguring the root filesystem in place, as in the LUKS example above, you can resize the existing partition using the
variant: fcos version: 1.2.0 storage: disks: - device: /dev/vda partitions: - label: root number: 4 # 0 means to use all available space size_mib: 0 resize: true luks: - name: root device: /dev/disk/by-partlabel/root clevis: tpm2: true wipe_volume: true filesystems: - device: /dev/mapper/root format: xfs wipe_filesystem: true label: root
This example configures a mirrored boot disk with a TPM2-encrypted root filesystem, overrides the sizes of the automatically-generated root partition replicas, and adds an encrypted mirrored
/var partition which consumes the remainder of the disks.
variant: fcos version: 1.3.0 boot_device: luks: tpm2: true mirror: devices: - /dev/sda - /dev/sdb storage: disks: - device: /dev/sda partitions: # Override size of root partition on first disk, via the label # generated for boot_device.mirror - label: root-1 size_mib: 8192 # Add a new partition filling the remainder of the disk - label: var-1 - device: /dev/sdb partitions: # Similarly for second disk - label: root-2 size_mib: 8192 - label: var-2 raid: - name: md-var level: raid1 devices: - /dev/disk/by-partlabel/var-1 - /dev/disk/by-partlabel/var-2 luks: - name: var device: /dev/md/md-var # No key material is specified, so a random key will be generated # and stored in the root filesystem filesystems: - device: /dev/mapper/var path: /var label: var format: xfs wipe_filesystem: true with_mount_unit: true
All Fedora CoreOS systems start with the same disk image which varies slightly between architectures based on what is needed for bootloading. On first boot the root filesystem is expanded to fill the rest of the disk. The disk image can be customized using Fedora CoreOS Configs to repartition the disk and create/reformat filesystems. Bare metal installations are not different; the installer only copies the raw image to the target disk and injects the specified config into
/boot for use on first boot.
|See Reconfiguring the root filesystem for examples regarding the supported changes to the root partition.|
Using partition numbers to refer to specific partitions is discouraged and labels or UUIDs should be used instead. Fedora CoreOS reserves the
esp-<number> labels, and the
md-root RAID device names. Creating partitions, filesystems, or RAID devices with those labels is not supported.
The x86_64 disk image is GPT formatted with a protective MBR. It supports booting via both BIOS and UEFI (including Secure Boot).
The partition table layout has changed over time. The current layout is:
Contains BIOS GRUB image
Contains EFI GRUB image and Secure Boot shim
Contains GRUB configuration, kernel/initramfs images
Contains the root filesystem
The EFI-SYSTEM partition can be deleted or reformatted when BIOS booting. Similarly, the BIOS-BOOT partition can be deleted or reformatted when EFI booting.
Fedora CoreOS uses OSTree, which is a system for managing multiple bootable operating system trees that share storage. This is distinct from e.g. Container Linux which used a dual partition system. In Fedora CoreOS each operating system version is part of the
/ filesystem. All deployments share the same
/var which can be on the same filesystem, or mounted separately.
This shows the default mountpoints for a Fedora CoreOS system installed on a
$ findmnt --real # Some details are elided TARGET SOURCE FSTYPE OPTIONS / /dev/vda4[/ostree/deploy/fedora-coreos/deploy/$hash] xfs rw |-/sysroot /dev/vda4 xfs ro |-/etc /dev/vda4[/ostree/deploy/fedora-coreos/deploy/$hash/etc] xfs rw |-/usr /dev/vda4[/ostree/deploy/fedora-coreos/deploy/$hash/usr] xfs ro |-/var /dev/vda4[/ostree/deploy/fedora-coreos/deploy/var] xfs rw `-/boot /dev/vda3 ext4 rw
The EFI System Partition was formerly mounted on
/boot/efi, but this is no longer the case. On systems configured with boot device mirroring, there are independent EFI partitions on each constituent disk.
As OSTree is used to manage all files belonging to the operating system, the
/usr mountpoints are not writable. Any changes to the operating system should be applied via
/boot mountpoint and EFI System Partition are managed by
bootupd, and changes must not be directly performed by an administrator in those filesystems.
/boot is not yet mounted as read only but this is expected to change in the future.
Adding top level directories (i.e.
/foo) is currently unsupported and disallowed by the immutable attribute.
/ (as in the root of the filesystem in the
root partition) is mounted readonly in
/sysroot and must not be accessed or modified directly.
The only supported writable locations are
/etc should contain only configuration files and is not expected to store data. All data must be kept under
/var and will not be touched by system upgrades. Traditional places that might hold state (e.g.
/srv) are symlinks to directories in
A GRUB menu entry is created for each version of Fedora CoreOS currently available on a system. This menu entry references an
ostree deployment which consist of a Linux kernel, an initramfs and a hash linking to an
ostree commit (passed via the
ostree= kernel argument). During bootup,
ostree will read this kernel argument to determine which deployment to use as the root filesystem. Each update or change to the system (package installation, addition of kernel arguments) creates a new deployment. This enables rolling back to a previous deployment if the update causes problems.