Blob Blame History Raw
% CONTAINERS-TRANSPORTS(5) Containers Transports Man Page
% Valentin Rothberg
% April 2019


containers-transports - description of supported transports for copying and storing container images


Tools which use the containers/image library, including skopeo(1), buildah(1), podman(1), all share a common syntax for referring to container images in various locations.
The general form of the syntax is _transport:details_, where details are dependent on the specified transport, which are documented below.

### **containers-storage:** [storage-specifier]{image-id|docker-reference[@image-id]}

An image located in a local containers storage.
The format of _docker-reference_ is described in detail in the **docker** transport.

The _storage-specifier_ allows for referencing storage locations on the file system and has the format `[[driver@]root[+run-root][:options]]` where the optional `driver` refers to the storage driver (e.g., overlay or btrfs) and where `root` is an absolute path to the storage's root directory.
The optional `run-root` can be used to specify the run directory of the storage where all temporary writable content is stored.
The optional `options` are a comma-separated list of driver-specific options.
Please refer to containers-storage.conf(5) for further information on the drivers and supported options.

### **dir:**_path_

An existing local directory _path_ storing the manifest, layer tarballs and signatures as individual files.
This is a non-standardized format, primarily useful for debugging or noninvasive container inspection.

### **docker://**_docker-reference_

An image in a registry implementing the "Docker Registry HTTP API V2".
By default, uses the authorization state in `$XDG_RUNTIME_DIR/containers/auth.json`, which is set using podman-login(1).
If the authorization state is not found there, `$HOME/.docker/config.json` is checked, which is set using docker-login(1).
The containers-registries.conf(5) further allows for configuring various settings of a registry.

Note that a _docker-reference_ has the following format: `name[:tag|@digest]`.
While the docker transport does not support both a tag and a digest at the same time some formats like containers-storage do.
Digests can also be used in an image destination as long as the manifest matches the provided digest.
The digest of images can be explored with skopeo-inspect(1).
If `name` does not contain a slash, it is treated as ``.
Otherwise, the component before the first slash is checked if it is recognized as a `hostname[:port]` (i.e., it contains either a . or a :, or the component is exactly localhost).
If the first component of name is not recognized as a `hostname[:port]`, `name` is treated as ``.

### **docker-archive:**_path[:docker-reference]_

An image is stored in the docker-save(1) formatted file.
_docker-reference_ is only used when creating such a file, and it must not contain a digest.
It is further possible to copy data to stdin by specifying `docker-archive:/dev/stdin` but note that the used file must be seekable.

### **docker-daemon:**_docker-reference|algo:digest_

An image stored in the docker daemon's internal storage.
The image must be specified as a _docker-reference_ or in an alternative _algo:digest_ format when being used as an image source.
The _algo:digest_ refers to the image ID reported by docker-inspect(1).

### **oci:**_path[:tag]_

An image compliant with the "Open Container Image Layout Specification" at _path_.
Using a _tag_ is optional and allows for storing multiple images at the same _path_.

### **oci-archive:**_path[:tag]_

An image compliant with the "Open Container Image Layout Specification" stored as a tar(1) archive at _path_.

### **ostree:**_docker-reference[@/absolute/repo/path]_

An image in the local ostree(1) repository.
_/absolute/repo/path_ defaults to _/ostree/repo_.

## Examples

The following examples demonstrate how some of the containers transports can be used.
The examples use skopeo-copy(1) for copying container images.

**Copying an image from one registry to another**:
$ skopeo copy docker:// docker://localhost:5000/alpine:latest

**Copying an image from a running Docker daemon to a directory in the OCI layout**:
$ mkdir alpine-oci
$ skopeo copy docker-daemon:alpine:latest oci:alpine-oci
$ tree alpine-oci
├── blobs
│   └── sha256
│       ├── 83ef92b73cf4595aa7fe214ec6747228283d585f373d8f6bc08d66bebab531b7
│       ├── 9a6259e911dcd0a53535a25a9760ad8f2eded3528e0ad5604c4488624795cecc
│       └── ff8df268d29ccbe81cdf0a173076dcfbbea4bb2b6df1dd26766a73cb7b4ae6f7
├── index.json
└── oci-layout

2 directories, 5 files

**Copying an image from a registry to the local storage**:
$ skopeo copy docker:// containers-storage:alpine:latest


docker-login(1), docker-save(1), ostree(1), podman-login(1), skopeo-copy(1), skopeo-inspect(1), tar(1), container-registries.conf(5), containers-storage.conf(5)


Miloslav Trmač <>
Valentin Rothberg <>