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CONTAINERS-TRANSPORTS(5) Man CONTAINERS-TRANSPORTS(5) 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), buil- dah(1), podman(1), all share a common syntax for referring to container im- ages in various locations. The general form of the syntax is transport:de- tails, 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-ref- erence 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 op- tional 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 contain- ers-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, primar- ily 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/contain- ers/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 al- lows for configuring various settings of a registry. Note that a docker-reference has the following format: name[:tag | @di- gest]. 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 pro- vided 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 recog- nized as a hostname <i.e., it contains either a `.` or a `:`, or the compo- nent is exactly `localhost`>. If the first component of name is not recog- nized 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 pro- vided 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 ac- cess untagged images). If neither docker-reference nor @_source_index is specified when reading an archive, the archive must contain exactly one im- age. 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|@source-index}] 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 : charac- ters 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. For reading images, @source-index is a zero-based index in manifest (to access untagged images). If neither reference nor @_source_index is specified when reading an image, the path must contain exactly one image. oci-archive:path[:reference] An image in a tar(1) archive with contents compliant with the "Open Con- tainer 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 pro- vided image. The path value terminates at the first : character; any further : charac- ters 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. 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/ aaa blobs aA A aaa sha256 aA A aaa 83ef92b73cf4595aa7fe214ec6747228283d585f373d8f6bc08d66bebab531b7 aA A aaa 9a6259e911dcd0a53535a25a9760ad8f2eded3528e0ad5604c4488624795cecc aA A aaa ff8df268d29ccbe81cdf0a173076dcfbbea4bb2b6df1dd26766a73cb7b4ae6f7 aaa index.json aaa 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), podman-login(1), skopeo-copy(1), skopeo- inspect(1), tar(1), container-registries.conf(5), containers-stor- age.conf(5) AUTHORS Miloslav TrmaA mitr@redhat.com <mailto:mitr@redhat.com> Valentin Rothberg rothberg@redhat.com <mailto:rothberg@redhat.com> Transports Containers CONTAINERS-TRANSPORTS(5)
NAME | DESCRIPTION | Examples | SEE ALSO | AUTHORS
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