What is the equivalent of docker volumes in containerd?

Question

In Docker, we can configure persistent storage via volumes. In Docker cli, we use "docker volume":

$ docker volume --help

Usage:  docker volume COMMAND

Manage volumes

Commands:
  create      Create a volume
  inspect     Display detailed information on one or more volumes
  ls          List volumes
  prune       Remove all unused local volumes
  rm          Remove one or more volumes

Run 'docker volume COMMAND --help' for more information on a command.

It looks like the containerd cli (ctr) doesn't have an equivalent item. They do have content:

$ ctr content --help
NAME:
   ctr content - manage content

USAGE:
   ctr content command [command options] [arguments...]

COMMANDS:
   active                   display active transfers
   delete, del, remove, rm  permanently delete one or more blobs
   edit                     edit a blob and return a new digest
   fetch                    fetch all content for an image into containerd
   fetch-object             retrieve objects from a remote
   get                      get the data for an object
   ingest                   accept content into the store
   list, ls                 list all blobs in the store
   push-object              push an object to a remote
   label                    add labels to content

OPTIONS:
   --help, -h  show help

There is also snapshot:

$ ctr snapshot --help
NAME:
   ctr snapshots - manage snapshots

USAGE:
   ctr snapshots command [command options] [arguments...]

COMMANDS:
   commit            commit an active snapshot into the provided name
   diff              get the diff of two snapshots. the default second snapshot is the first snapshot's parent.
   info              get info about a snapshot
   list, ls          list snapshots
   mounts, m, mount  mount gets mount commands for the snapshots
   prepare           prepare a snapshot from a committed snapshot
   remove, rm        remove snapshots
   label             add labels to content
   tree              display tree view of snapshot branches
   unpack            unpack applies layers from a manifest to a snapshot
   usage             usage snapshots
   view              create a read-only snapshot from a committed snapshot

OPTIONS:
   --snapshotter value  snapshotter name. Empty value stands for the default value. [$CONTAINERD_SNAPSHOTTER]
   --help, -h           show help

Which is the equivalent? And how should I be interpreting the results from ctr cli outputs?

Answer 1

From: https://containerd.io/scope/

containerd is designed to be embedded into a larger system, hence it only includes a barebone CLI (ctr) specifically for development and debugging purpose, with no mandate to be human-friendly, and no guarantee of interface stability over time.

Have a look at runc: https://danishpraka.sh/2020/07/24/introduction-to-runc.html

runtime-spec

Specifying configuration options such as volume mounts, memory limits or uid:gid mapping while running a container with docker is as simple as specifying command line options to the docker command. While using runc, these configurations are passed to runc as a file. This configuration file, the runtime-spec, is a configuration standard put in place by the Open Container Initiative (OCI) to specify options for a container and is used by runc[2]. In simpler words, the runtime-spec is a JSON file named config.json consisting of configurations pertaining to a specific container.