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% CONTAINERS-REGISTRIES.CONF(5) System-wide registry configuration file % Brent Baude % Aug 2017


containers-registries.conf - Syntax of System Registry Configuration File


The CONTAINERS-REGISTRIES configuration file is a system-wide configuration file for container image registries. The file format is TOML.

By default, the configuration file is located at /etc/containers/registries.conf.



VERSION 2 is the latest format of the registries.conf and is currently in beta. This means in general VERSION 1 should be used in production environments for now.


unqualified-search-registries : An array of host[:port] registries to try when pulling an unqualified image, in order.


The bulk of the configuration is represented as an array of [[registry]] TOML tables; the settings may therefore differ among different registries as well as among different namespaces/repositories within a registry.

Choosing a [[registry]] TOML table

Given an image name, a single [[registry]] TOML table is chosen based on its prefix field.

prefix : A prefix of the user-specified image name, i.e. using one of the following formats: - host[:port] - host[:port]/namespace[/namespace…] - host[:port]/namespace[/namespace…]/repo - host[:port]/namespace[/namespace…]/repo(:_tag|@digest)

The user-specified image name must start with the specified `prefix` (and continue
with the appropriate separator) for a particular `[[registry]]` TOML table to be
considered; (only) the TOML table with the longest match is used.

As a special case, the `prefix` field can be missing; if so, it defaults to the value
of the `location` field (described below).

Per-namespace settings

insecure : true or false. By default, container runtimes require TLS when retrieving images from a registry. If insecure is set to true, unencrypted HTTP as well as TLS connections with untrusted certificates are allowed.

blocked : true or false. If true, pulling images with matching names is forbidden.

Remapping and mirroring registries

The user-specified image reference is, primarily, a "logical" image name, always used for naming the image. By default, the image reference also directly specifies the registry and repository to use, but the following options can be used to redirect the underlying accesses to different registry servers or locations (e.g. to support configurations with no access to the internet without having to change Dockerfiles, or to add redundancy).

location : Accepts the same format as the prefix field, and specifies the physical location of the prefix-rooted namespace.

By default, this equal to `prefix` (in which case `prefix` can be omitted and the
`[[registry]]` TOML table can only specify `location`).

Example: Given
prefix = ""
location = ""
requests for the image `` will actually work with the
`` image.

mirror : An array of TOML tables specifying (possibly-partial) mirrors for the prefix-rooted namespace.

The mirrors are attempted in the specified order; the first one that can be
contacted and contains the image will be used (and if none of the mirrors contains the image,
the primary location specified by the `registry.location` field, or using the unmodified
user-specified reference, is tried last).

Each TOML table in the `mirror` array can contain the following fields, with the same semantics
as if specified in the `[[registry]]` TOML table directly:
- `location`
- `insecure`

mirror-by-digest-only : true or false. If true, mirrors will only be used during pulling if the image reference includes a digest. Referencing an image by digest ensures that the same is always used (whereas referencing an image by a tag may cause different registries to return different images if the tag mapping is out of sync).

Note that if this is `true`, images referenced by a tag will only use the primary
registry, failing if that registry is not accessible.

Note: Redirection and mirrors are currently processed only when reading images, not when pushing to a registry; that may change in the future.


unqualified-search-registries = [""]

prefix = ""
insecure = false
blocked = false
location = ""

location = "example-mirror-0.local/mirror-for-foo"

location = "example-mirror-1.local/mirrors/foo"
insecure = true

Given the above, a pull of will try: 1. example-mirror-0.local/mirror-for-foo/image:latest 2. example-mirror-1.local/mirrors/foo/image:latest 3.

in order, and use the first one that exists.


VERSION 1 can be used as alternative to the VERSION 2, but it does not support using registry mirrors, longest-prefix matches, or location rewriting.

The TOML format is used to build a simple list of registries under three categories:, registries.insecure, and registries.block. You can list multiple registries using a comma separated list.

Search registries are used when the caller of a container runtime does not fully specify the container image that they want to execute. These registries are prepended onto the front of the specified container image until the named image is found at a registry.

Note that insecure registries can be used for any registry, not just the registries listed under search.

The registries.insecure and registries.block lists have the same meaning as the insecure and blocked fields in VERSION 2.


The following example configuration defines two searchable registries, one insecure registry, and two blocked registries.

registries = ['', '']

registries = ['']

registries = ['', '']


Mar 2019, Added additional configuration format by Sascha Grunert

Aug 2018, Renamed to containers-registries.conf(5) by Valentin Rothberg

Jun 2018, Updated by Tom Sweeney

Aug 2017, Originally compiled by Brent Baude

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