Snapshotters manage the snapshots of the container filesystems.

The available snapshotters can be inspected by running ctr plugins ls or nerdctl info.

Generic:

• overlayfs (default): OverlayFS. This driver is akin to Docker/Moby's "overlay2" storage driver, but containerd's implementation is not called "overlay2".
• native: Native file copying driver. Akin to Docker/Moby's "vfs" driver.

Block-based:

• blockfile: A driver using raw block files for each snapshot. Block files are copied from a parent or base empty block file. Mounting requires a virtual machine or support for loopback mounts.
• devmapper: ext4/xfs device mapper. See devmapper.md.

Filesystem-specific:

• btrfs: btrfs. Needs the plugin root (/var/lib/containerd/io.containerd.snapshotter.v1.btrfs) to be mounted as btrfs.
• zfs: ZFS. Needs the plugin root (/var/lib/containerd/io.containerd.snapshotter.v1.zfs) to be mounted as ZFS. See also https://github.com/containerd/zfs .

Deprecated:

• aufs: AUFS. Deprecated since containerd 1.5. Removed in containerd 2.0. See also https://github.com/containerd/aufs .

• fuse-overlayfs: FUSE-OverlayFS Snapshotter
• nydus: Nydus Snapshotter
• overlaybd: OverlayBD Snapshotter
• stargz: Stargz Snapshotter

Mounts can optionally specify a target to describe submounts in the container's rootfs. For example, if the snapshotter wishes to bind mount to a subdirectory ontop of an overlayfs mount, they can return the following mounts:

[
    {
        "type": "overlay",
        "source": "overlay",
        "options": [
            "workdir=...",
            "upperdir=...",
            "lowerdir=..."
        ]
    },
    {
        "type": "bind",
        "source": "/path/on/host",
        "target": "/path/inside/container",
        "options": [
            "ro",
            "rbind"
        ]
    }
]

However, the mountpoint /path/inside/container needs to exist for the bind mount, so one of the previous mounts must be responsible for providing that directory in the rootfs. In this case, one of the lower dirs of the overlay has that directory to enable the bind mount.