Behind the seemingly simple act of running a container lies a powerful abstraction layer: the container filesystem. To ensure portability and performance, container runtimes use several powerful mechanisms and command-line tools that are part of, or integrated with, the Container Runtime Interface (CRI). At the heart of container filesystem management are the cri-tools suite and the internal mechanisms of runtimes like containerd and CRI-O.
The path to these directories is stored in the runtime’s metadata, and are often created to simplify access. For instance, CRI-O creates:
CRI File System tools are primarily used to pack, compress, and manage game assets in the format , which is a proprietary archive format developed by CRI Middleware . 🛠️ Official CRI File System Tools
💡 : If a file won't open, some users have success by renaming the extension to .zip and using 7-Zip, though this only works for uncompressed or simple archives . How to Extract CPK Files (CRI Packed File Maker) cri file system tools link
The container runtime follows the CRI logging format, sending stdout/stderr from applications to files.
| Type | Description | Tool responsibility | |--------------|-----------------------------------------------|----------------------------------| | OverlayFS | Union filesystem for image layers | containerd/cri-o image service | | bind mount | Host directory exposed to container | CRI volume manager | | tmpfs | In-memory filesystem | crictl runp –runtime-options | | block device | Direct LVM or EBS mount | CSI driver invoked via CRI |
Hard links are not just for files—they can be used at the directory level (via cp -al ) to create instant clones of container root filesystems without copying data. This is a powerful technique when you need multiple copies of a snapshot for testing. Behind the seemingly simple act of running a
Without robust CRI filesystem tools, containers would leak storage, corrupt layers, or fail to unmount after pod termination.
Container runtimes use snapshotters (like OverlayFS, Btrfs, or ZFS) to handle the "graph" of container images. These tools manage the COW (Copy-on-Write) layers, ensuring that multiple containers can share the same base image without interfering with one another's data. Impact on Infrastructure
If your cluster uses containerd , the storage is managed via content-addressable namespaces. The path to these directories is stored in
Which is your cluster currently running ( containerd , CRI-O , or Mirantis)?
Managing CPK files typically follows a straightforward workflow: Preparation
CRI-O exposes an HTTP API via a Unix socket, allowing you to query the storage driver being used in real-time.
To manage or create these file systems, you will primarily use the following tools: