NAME
containers-transports - description of supported transports for copying and storing container images
DESCRIPTION
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 docker.io/library/name. 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.io/name.
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.io/library/alpine:latest 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
test-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://docker.io/library/alpine:latest containers-storage:alpine:latest
SEE ALSO
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)
AUTHORS
Miloslav Trmač ⟨ mitr [AT] redhat.com⟩ Valentin Rothberg ⟨ rothberg [AT] redhat.com⟩