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Tool to check generic rules/best-practices for containers/images/dockerfiles.

Project description


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Tool to check generic rules and best-practices for container images and dockerfiles.

For more information, please check our documentation on



  • Validate a selected artifact against a ruleset.
  • Artifacts can be container images and dockerfiles.
  • We provide a default ruleset we believe every container image should satisfy.
  • There is a ruleset to validate an artifact whether it complies to Fedora Container Guidelines
  • Colin can list available rulesets and list checks in a ruleset.
  • There is a python API available
  • Colin can be integrated into your workflow easily - it can provide results in json format.


Via pip

If you are on Fedora distribution, please install python3-pyxattr so you don't have to compile it yourself when getting it from PyPI.

$ pip3 install --user colin

colin is supported on python 3.6+ only.

On Fedora distribution

colin is packaged in official Fedora repositories:

$ dnf install -y colin


  • For checking image target-type, you have to install podman. If you need to check local docker images, you need to prefix your images with docker-daemon (e.g. colin check

  • If you want to use oci target, you need to install following tools:


$ colin --help
Usage: colin [OPTIONS] COMMAND [ARGS]...

  COLIN -- Container Linter

  -V, --version  Show the version and exit.
  -h, --help     Show this message and exit.

  check          Check the image/dockerfile (default).
  info           Show info about colin and its dependencies.
  list-checks    Print the checks.
  list-rulesets  List available rulesets.
$ colin check --help
Usage: colin check [OPTIONS] TARGET

  Check the image/dockerfile (default).

  -r, --ruleset TEXT           Select a predefined ruleset (e.g. fedora).
  -f, --ruleset-file FILENAME  Path to a file to use for validation (by
                               default they are placed in
  --debug                      Enable debugging mode (debugging logs, full
  --json FILENAME              File to save the output as json to.
  --stat                       Print statistics instead of full results.
  -s, --skip TEXT              Name of the check to skip. (this option is
  -t, --tag TEXT               Filter checks with the tag.
  -v, --verbose                Verbose mode.
  --checks-path DIRECTORY      Path to directory containing checks (default
  --pull                       Pull the image from registry.
  --target-type TEXT           Type of selected target (one of image,
                               dockerfile, oci). For oci, please specify
                               image name and path like this: oci:path:image
  --timeout INTEGER            Timeout for each check in seconds.
  --insecure                   Pull from an insecure registry (HTTP or invalid
  -h, --help                   Show this message and exit.

Let's give it a shot:

$ colin -f ./rulesets/fedora.json
PASS:Label 'architecture' has to be specified.
PASS:Label 'build-date' has to be specified.
FAIL:Label 'description' has to be specified.
PASS:Label 'distribution-scope' has to be specified.

Directly from git

It's possible to use colin directly from git:

$ git clone
$ cd colin

We can now run the analysis:

$ python3 -m colin.cli.colin -f ./rulesets/fedora.json
PASS:Label 'architecture' has to be specified.
PASS:Label 'build-date' has to be specified.
FAIL:Label 'description' has to be specified.
PASS:Label 'distribution-scope' has to be specified.

Exit codes

Colin can exit with several codes:

  • 0 --> OK
  • 1 --> error in the execution
  • 2 --> CLI error, wrong parameters
  • 3 --> at least one check failed

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