Haskell Dockerfile Linter

A smarter Dockerfile linter that helps you build best practice Docker images. The linter is parsing the Dockerfile into an AST and performs rules on top of the AST. It is standing on the shoulders of ShellCheck to lint the Bash code inside RUN instructions.

🌐 Check the online version on hadolint.github.io/hadolint

How to use

You can run hadolint locally to lint your Dockerfile.

hadolint <Dockerfile>
hadolint --ignore DL3003 --ignore DL3006 <Dockerfile> # exclude specific rules
hadolint --trusted-registry my-company.com:500 <Dockerfile> # Warn when using untrusted FROM images

Docker comes to the rescue to provide an easy way how to run hadolint on most platforms. Just pipe your Dockerfile to docker run:

$ docker run --rm -i hadolint/hadolint < Dockerfile
# OR
$ docker run --rm -i ghcr.io/hadolint/hadolint < Dockerfile

or if you are using Windows PowerShell:

> cat .\Dockerfile | docker run --rm -i hadolint/hadolint

Install

You can download prebuilt binaries for OSX, Windows and Linux from the latest release page. However, if it doesn't work for you, please fall back to Docker, brew or source installation.

If you are on OSX you can use brew to install hadolint.

brew install hadolint

On Windows you can use scoop to install hadolint.

scoop install hadolint

As shown before, hadolint is available as a Docker container:

docker pull hadolint/hadolint
# OR
docker pull ghcr.io/hadolint/hadolint

If you need a Docker container with shell access, use the Debian or Alpine variants of the Docker image:

docker pull hadolint/hadolint:latest-debian
# OR 
docker pull hadolint/hadolint:latest-alpine
# OR
docker pull ghcr.io/hadolint/hadolint:latest-debian
# OR
docker pull ghcr.io/hadolint/hadolint:latest-alpine

You can also build hadolint locally. You need Haskell and the stack build tool to build the binary.

git clone https://github.com/hadolint/hadolint \
&& cd hadolint \
&& stack install

CLI

hadolint --help

hadolint - Dockerfile Linter written in Haskell

Usage: hadolint [-v|--version] [--no-fail] [--no-color] [-c|--config FILENAME] 
                [-V|--verbose] [-f|--format ARG] [DOCKERFILE...] 
                [--error RULECODE] [--warning RULECODE] [--info RULECODE] 
                [--style RULECODE] [--ignore RULECODE] 
                [--trusted-registry REGISTRY (e.g. docker.io)] 
                [--require-label LABELSCHEMA (e.g. maintainer:text)] 
                [--strict-labels] [-t|--failure-theshold THRESHOLD]
  Lint Dockerfile for errors and best practices

Available options:
  -h,--help                Show this help text
  -v,--version             Show version
  --no-fail                Don't exit with a failure status code when any rule
                           is violated
  --no-color               Don't colorize output
  -c,--config FILENAME     Path to the configuration file
  -V,--verbose             Enables verbose logging of hadolint's output to
                           stderr
  -f,--format ARG          The output format for the results [tty | json |
                           checkstyle | codeclimate | gitlab_codeclimate |
                           codacy] (default: tty)
  --error RULECODE         Make the rule `RULECODE` have the level `error`
  --warning RULECODE       Make the rule `RULECODE` have the level `warning`
  --info RULECODE          Make the rule `RULECODE` have the level `info`
  --style RULECODE         Make the rule `RULECODE` have the level `style`
  --ignore RULECODE        A rule to ignore. If present, the ignore list in the
                           config file is ignored
  --trusted-registry REGISTRY (e.g. docker.io)
                           A docker registry to allow to appear in FROM
                           instructions
  --require-label LABELSCHEMA (e.g. maintainer:text)
                           The option --require-label=label:format makes
                           Hadolint check that the label `label` conforms to
                           format requirement `format`
  --strict-labels          Do not permit labels other than specified in
                           `label-schema`
  -t,--failure-theshold THRESHOLD
                           Exit with failure code only when rules with a
                           severity above THRESHOLD are violated. Accepted
                           values: [error | warning | info | style | ignore |
                           none] (default: info)

Configure

Configuration files can be used globally or per project. By default, hadolint will look for a configuration file in the current directory with the name .hadolint.yaml or .hadolint.yml

hadolint full yaml config file schema

failure-threshold: string               # name of threshold level (error | warning | info | style | ignore | none)                
format: string                          # Output format (tty | json | checkstyle | codeclimate | gitlab_codeclimate | codacy)
ignored: [string]                       # list of rules
label-schema:                           # See Linting Labels below for specific label-schema details
  author: string                        # Your name
  contact: string                       # email address
  created: timestamp                    # rfc3339 datetime
  version: string                       # semver
  documentation: string                 # url
  git-revision: string                  # hash
  license: string                       # spdx
no-color: boolean                       # true | false
no-fail: boolean                        # true | false
override:
  error: [string]                       # list of rules
  warning: [string]                     # list of rules
  info: [string]                        # list of rules
  style: [string]                       # list of rules
strict-labels: boolean                  # true | false
trustedRegistries: string | [string]    # registry or list of registries

hadolint supports specifying the ignored rules using a configuration file. The configuration file should be in yaml format. This is one valid configuration file as an example:

ignored:
  - DL3000
  - SC1010

Additionally, hadolint can warn you when images from untrusted repositories are being used in Dockerfiles, you can append the trustedRegistries keys to the configuration file as shown below:

ignored:
  - DL3000
  - SC1010

trustedRegistries:
  - docker.io
  - my-company.com:5000

If you want to override the severity of specific rules, you can do that too:

override:
  error:
    - DL3001
    - DL3002
  warning:
    - DL3042
    - DL3033
  info:
    - DL3032
  style:
    - DL3015

failure-threshold Exit with failure code only when rules with a severity above THRESHOLD are violated (Available in v2.6.0+)

failure-threshold: info
warning:
    - DL3042
    - DL3033
  info:
    - DL3032

The global configuration file should be placed in the folder specified by XDG_CONFIG_HOME, with the name hadolint.yaml or hadolint.yml. In summary, the following locations are valid for the configuration file, in order or preference:

• $PWD/.hadolint.yaml
• $XDG_CONFIG_HOME/hadolint.yaml
• ~/.config/hadolint.yaml

In windows, the %LOCALAPPDATA% environment variable is used instead of XDG_CONFIG_HOME

Additionally, you can pass a custom configuration file in the command line with the --config option

hadolint --config /path/to/config.yaml Dockerfile

To pass a custom configuration file (using relative or absolute path) to a container, use the following command:

docker run --rm -i -v /your/path/to/hadolint.yaml:/.config/hadolint.yaml hadolint/hadolint < Dockerfile
# OR
docker run --rm -i -v /your/path/to/hadolint.yaml:/.config/hadolint.yaml ghcr.io/hadolint/hadolint < Dockerfile

Inline ignores

It is also possible to ignore rules by using a special comment directly above the Dockerfile instruction you want to make an exception for. Ignore rule comments look like # hadolint ignore=DL3001,SC1081. For example:

# hadolint ignore=DL3006
FROM ubuntu

# hadolint ignore=DL3003,SC1035
RUN cd /tmp && echo "hello!"

Inline ignores will only work if place directly above the instruction.

Linting Labels

Hadolint has the ability to check that specific labels be present and conform to a predefined label schema. First a label schema must be defined either via commandline:

hadolint --require-label author:text --require-label version:semver Dockerfile

or via config file:

label-schema:
  author: text
  contact: email
  created: rfc3339
  version: semver
  documentation: url
  git-revision: hash
  license: spdx

The value of a label can be either of text, url, semver, hash or rfc3339: | Schema | Description | |:--------|:---------------------------------------------------| | text | Anything | | rfc3339 | A time, formatted according to RFC 3339 | | semver | A semantic version | | url | A URI as described in RFC 3986 | | hash | Either a short or a long Git hash | | spdx | An SPDX license identifier | | email | An email address conforming to RFC 5322 |

By default, Hadolint ignores any label not specified in the label schema. To warn on such additional labels, turn on strict labels:

hadolint --strict-labels --require-label version:semver Dockerfile

or in the config file:

strict-labels: true

When strict labels is enabled, but no label schema has been specified, Hadolint will warn if any label is present.

Note on dealing with variables in labels

It is a common pattern to fill the value of a label not statically, but rather dynamically at build time by using a variable:

FROM debian:buster
ARG VERSION="du-jour"
LABEL version="${VERSION}"

To allow this, the label schema must specify text as value for that label:

label-schema:
  version: text

Integrations

To get most of hadolint it is useful to integrate it as a check to your CI or to your editor, or as a pre-commit hook, to lint your Dockerfile as you write it. See our Integration docs.

• Code Review Platform Integrations
• Continuous Integrations
• Editor Integrations
• Version Control Integrations

Rules

An incomplete list of implemented rules. Click on the error code to get more detailed information.

• Rules with the prefix DL originate from hadolint. Take a look at Rules.hs to find the implementation of the rules.

• Rules with the SC prefix originate from ShellCheck (Only the most common rules are listed, there are dozens more)

Please create an issue if you have an idea for a good rule.

Develop

If you are an experienced Haskeller we would be really thankful if you would tear our code apart in a review.

Setup

1. Clone repository

   git clone --recursive git@github.com:hadolint/hadolint.git
   

2. Install the dependencies

   stack install
   

REPL

The easiest way to try out the parser is using the REPL.

# start the repl
stack repl
# overload strings to be able to use Text
:set -XOverloadedStrings
# import parser library
import Language.Docker
# parse instruction and look at AST representation
parseText "FROM debian:jessie"

Tests

Run unit tests.

stack test

Run integration tests.

./integration_test.sh

AST

Dockerfile syntax is fully described in the Dockerfile reference. Just take a look at Syntax.hs in the language-docker project to see the AST definition.

Alternatives

• RedCoolBeans/dockerlint
• projectatomic/dockerfile_lint