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overlay.md

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Configuration

overlay type

Specifies the configuration for overlay filesystem.

Example:

os:
  overlays:
  - mountPoint: /media
    lowerDirs:
    - /media
    - /home
    upperDir: /overlays/media/upper
    workDir: /overlays/media/work

mountPoint [string]

The directory where the combined view of the upperDir and lowerDir will be mounted. This is the location where users will see the merged contents of the overlay filesystem. It is common for the mountPoint to be the same as the lowerDir. But this is not required.

Example: /etc

lowerDirs [string[]]

A list of directories that act as the read-only layers in the overlay filesystem. They contain the base files and directories which will be overlaid by the upperDir.

Example:

lowerDirs: 
- /etc

upperDir [string]

Required.

This directory is the writable layer of the overlay filesystem. Any modifications, such as file additions, deletions, or changes, are made in the upperDir. These changes are what make the overlay filesystem appear different from the lowerDir alone.

Example: /var/overlays/etc/upper

workDir [string]

Required.

This directory is used for preparing files before they are merged into the upperDir. It needs to be on the same filesystem as the upperDir and is used for temporary storage by the overlay filesystem to ensure atomic operations. The workDir should not be directly accessed by users.

Example: /var/overlays/etc/work

isInitrdOverlay [bool]

A boolean flag indicating that this overlay should be provisioned by the initramfs before the pivot to the root filesystem. This should be set to true for overlays targeting fundamental system directories such as /etc.

Setting this value to true will result to the following changes to the overlay:

  • The lower, upper, and work directories' paths will have the /sysroot prefix added to them, since that is the path of the root filesystem before the pivot.

  • The mount options x-initrd.mount,x-systemd.wanted-by=initrd-fs.target will be added to the overlay.

Default value: false.

Example:

storage:
  disks:
  bootType: efi
  - partitionTableType: gpt
    partitions:
    - id: esp
      type: esp
      size: 8M

    - id: rootfs
      label: rootfs
      size: 2G

    - id: var
      size: 2G

  filesystems:
  - deviceId: esp
    type: fat32
    mountPoint:
      path: /boot/efi
      options: umask=0077

  - deviceId: rootfs
    type: ext4
    mountPoint: /

  - deviceId: var
    type: ext4
    mountPoint:
      path: /var
      options: defaults,x-initrd.mount

os:
  bootloader:
    resetType: hard-reset

  overlays:
  - mountPoint: /etc
    lowerDirs:
    - /etc
    upperDir: /var/overlays/etc/upper
    workDir: /var/overlays/etc/work
    isInitrdOverlay: true
    mountDependencies:
    - /var

mountDependencies [string[]]

Specifies a list of directories that must be mounted before this overlay. Each directory in the list should be mounted and available before the overlay filesystem is mounted.

This is an optional argument.

Example:

mountDependencies: 
- /var

Important: If any directory specified in mountDependencies needs to be available during the initrd phase, you must ensure that this directory's mount configuration in the filesystems section includes the x-initrd.mount option.

For example:

filesystems:
- deviceId: var
  type: ext4
  mountPoint:
    path: /var
    options: defaults,x-initrd.mount

mountOptions [string]

A string of additional mount options that can be applied to the overlay mount. Multiple options should be separated by commas.

This is an optional argument.

Example: noatime,nodiratime