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ext4_drives

List of ext4-formatted storage devices to be automatically mounted when available.

Each drive gets a systemd mount unit with nofail and automount, so a missing or late drive never blocks the boot, and an SELinux context that lets rootless containers read and write it.

ext4_drives[].uuid

The UUID of the block device to mount. It uniquely identifies a filesystem on a specific partition (i.e. a block device).

You can use:

lsblk

to list connected block devices and partitions, then, replacing xxx as appropriate:

sudo blkid /dev/xxx

to obtain the UUID of the desired filesystem.

  • Type: String
  • Purpose: Ensures consistent device identification across reboots.

ext4_drives[].mount_point

Filesystem path where the drive will be mounted.

On FCOS, the root filesystem is immutable and writable storage is limited to /var. For this reason, mount points must reside under /var.

  • Type: Absolute path
  • Example: /var/hdd

ext4_drives[].placeholder_dirs

Directories to be created under the mount point on the host system.

These directories act as placeholders when the device is not present at boot, allowing containers that bind-mount these paths to start normally. If the device becomes available later, it will be mounted automatically and its contents will transparently shadow the placeholder directories.

  • Type: List of directory names
  • Purpose: Subdirectories of the mounted drive for which placeholders should exist.
  • Examples:
    • Movies
    • Shows
    • Music
    • Photos