1CONTAINERS-TRANSPORTS(5) Man CONTAINERS-TRANSPORTS(5)
2Valentin Rothberg April 2019
6
8 containers-transports - description of supported transports for copying
9 and storing container images
10
13 Tools which use the containers/image library, including skopeo(1),
14 buildah(1), podman(1), all share a common syntax for referring to con‐
15 tainer images in various locations. The general form of the syntax is
16 transport:details, where details are dependent on the specified trans‐
17 port, which are documented below.
18 containers-storage:[[storage-specifier]]{image-id|docker-reference[@image-
21 id]}
22 An image located in a local containers storage. The format of docker-
23 reference is described in detail in the docker transport.
24 The storage-specifier allows for referencing storage locations on the
27 file system and has the format [[driver@]root[+run-root][:options]]
28 where the optional driver refers to the storage driver (e.g., overlay
29 or btrfs) and where root is an absolute path to the storage's root di‐
30 rectory. The optional run-root can be used to specify the run direc‐
31 tory of the storage where all temporary writable content is stored.
32 The optional options are a comma-separated list of driver-specific op‐
33 tions. Please refer to containers-storage.conf(5) for further informa‐
34 tion on the drivers and supported options.
35 dir:path
38 An existing local directory path storing the manifest, layer tarballs
39 and signatures as individual files. This is a non-standardized format,
40 primarily useful for debugging or noninvasive container inspection.
41 docker://docker-reference
44 An image in a registry implementing the "Docker Registry HTTP API V2".
45 By default, uses the authorization state in $XDG_RUNTIME_DIR/contain‐
46 ers/auth.json, which is set using podman-login(1). If the authoriza‐
47 tion state is not found there, $HOME/.docker/config.json is checked,
48 which is set using docker-login(1). The containers-registries.conf(5)
49 further allows for configuring various settings of a registry.
50 Note that a docker-reference has the following format: name[:tag|@di‐
53 gest]. While the docker transport does not support both a tag and a
54 digest at the same time some formats like containers-storage do. Di‐
55 gests can also be used in an image destination as long as the manifest
56 matches the provided digest. The digest of images can be explored with
57 skopeo-inspect(1). If name does not contain a slash, it is treated as
58 docker.io/library/name. Otherwise, the component before the first
59 slash is checked if it is recognized as a hostname[:port] (i.e., it
60 contains either a . or a :, or the component is exactly localhost). If
61 the first component of name is not recognized as a hostname[:port],
62 name is treated as docker.io/name.
63 docker-archive:path[:{docker-reference|@source-index}]
66 An image is stored in the docker-save(1) formatted file. docker-refer‐
67 ence must not contain a digest. Alternatively, for reading archives,
68 @source-index is a zero-based index in archive manifest (to access un‐
69 tagged images). If neither docker-reference nor @_source_index is
70 specified when reading an archive, the archive must contain exactly one
71 image.
72 It is further possible to copy data to stdin by specifying docker-ar‐
75 chive:/dev/stdin but note that the used file must be seekable.
76 docker-daemon:docker-reference|algo:digest
79 An image stored in the docker daemon's internal storage. The image
80 must be specified as a docker-reference or in an alternative algo:di‐
81 gest format when being used as an image source. The algo:digest refers
82 to the image ID reported by docker-inspect(1).
83 oci:path[:reference]
86 An image compliant with the "Open Container Image Layout Specification"
87 at path. Using a reference is optional and allows for storing multiple
88 images at the same path.
89 oci-archive:path[:reference]
92 An image compliant with the "Open Container Image Layout Specification"
93 stored as a tar(1) archive at path.
94 ostree:docker-reference[@/absolute/repo/path]
97 An image in the local ostree(1) repository. /absolute/repo/path de‐
98 faults to /ostree/repo.
99
102 The following examples demonstrate how some of the containers trans‐
103 ports can be used. The examples use skopeo-copy(1) for copying con‐
104 tainer images.
105 Copying an image from one registry to another:
108 $ skopeo copy docker://docker.io/library/alpine:latest docker://localhost:5000/alpine:latest
111 Copying an image from a running Docker daemon to a directory in the OCI
115 layout:
116 $ mkdir alpine-oci
119 $ skopeo copy docker-daemon:alpine:latest oci:alpine-oci
120 $ tree alpine-oci
121 test-oci/
122 ├── blobs
123 │ └── sha256
124 │ ├── 83ef92b73cf4595aa7fe214ec6747228283d585f373d8f6bc08d66bebab531b7
125 │ ├── 9a6259e911dcd0a53535a25a9760ad8f2eded3528e0ad5604c4488624795cecc
126 │ └── ff8df268d29ccbe81cdf0a173076dcfbbea4bb2b6df1dd26766a73cb7b4ae6f7
127 ├── index.json
128 └── oci-layout
129 2 directories, 5 files
131 Copying an image from a registry to the local storage:
135 $ skopeo copy docker://docker.io/library/alpine:latest containers-storage:alpine:latest
138
142 docker-login(1), docker-save(1), ostree(1), podman-login(1), skopeo-
143 copy(1), skopeo-inspect(1), tar(1), container-registries.conf(5), con‐
144 tainers-storage.conf(5)
145
148 Miloslav Trmač mitr@redhat.com ⟨mailto:mitr@redhat.com⟩ Valentin Roth‐
149 berg rothberg@redhat.com ⟨mailto:rothberg@redhat.com⟩
150Transports Containers CONTAINERS-TRANSPORTS(5)