% CONTAINERS-TRANSPORTS 5 Containers Transports Man Page % Valentin Rothberg % April 2019 ## 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. The semantics of the image names ultimately depend on the environment where they are evaluated. For example: if evaluated on a remote server, image names might refer to paths on that server; relative paths are relative to the current directory of the image consumer. ### **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 docker transport supports pushing images without a tag or digest to a registry when the image name is suffixed with `@@unknown-digest@@`. The _name_`@@unknown-digest@@` reference format cannot be used with a reference that has a tag or 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_|`@`_source-index_}] An image is stored in the docker-save(1) formatted file. Unless a tool explicitly documents otherwise, a write to a **docker-archive:** destination completely overwrites _path_, replacing it with the single provided image. The _path_ can refer to a stream, e.g. `docker-archive:/dev/stdin`. _docker-reference_ must not contain a digest. Alternatively, for reading archives, `@`_source-index_ is a zero-based index in archive manifest (to access untagged images). If neither _docker-reference_ nor `@`_source_index is specified when reading an archive, the archive must contain exactly one image. ### **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_[`:`_reference_] An image in a directory structure compliant with the "Open Container Image Layout Specification" at _path_. The _path_ value terminates at the first `:` character; any further `:` characters are not separators, but a part of _reference_. The _reference_ is used to set, or match, the `org.opencontainers.image.ref.name` annotation in the top-level index. If _reference_ is not specified when reading an image, the directory must contain exactly one image. ### **oci-archive:**_path_[`:`_reference_] An image in a tar(1) archive with contents compliant with the "Open Container Image Layout Specification" at _path_. Unless a tool explicitly documents otherwise, a write to an **oci-archive:** destination completely overwrites _path_, replacing it with the single provided image. The _path_ value terminates at the first `:` character; any further `:` characters are not separators, but a part of _reference_. The _reference_ is used to set, or match, the `org.opencontainers.image.ref.name` annotation in the top-level index. If _reference_ is not specified when reading an archive, the archive must contain exactly one image. ### **ostree:**_docker-reference_[`@`_/absolute/repo/path_] An image in the local ostree(1) repository. _/absolute/repo/path_ defaults to `/ostree/repo`. ### **sif:**_path_ An image using the Singularity image format at _path_. Only reading images is supported, and not all scripts can be represented in the OCI format. ## 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 Valentin Rothberg