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
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
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
$ docker pull hadolint/hadolint:latest-alpine
# or
$ docker pull ghcr.io/hadolint/hadolint:latest-debian
$ 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
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
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
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
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.
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 |
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.
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
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
An incomplete list of implemented rules. Click on the error code to get more detailed information.
-
Rules with the prefix
DL
originate fromhadolint
. Take a look atRules.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.
Rule | Description |
---|---|
DL3000 | Use absolute WORKDIR. |
DL3001 | For some bash commands it makes no sense running them in a Docker container like ssh, vim, shutdown, service, ps, free, top, kill, mount, ifconfig. |
DL3002 | Last user should not be root. |
DL3003 | Use WORKDIR to switch to a directory. |
DL3004 | Do not use sudo as it leads to unpredictable behavior. Use a tool like gosu to enforce root. |
DL3005 | Do not use apt-get dist-upgrade. |
DL3006 | Always tag the version of an image explicitly. |
DL3007 | Using latest is prone to errors if the image will ever update. Pin the version explicitly to a release tag. |
DL3008 | Pin versions in apt-get install. |
DL3009 | Delete the apt-get lists after installing something. |
DL3010 | Use ADD for extracting archives into an image. |
DL3011 | Valid UNIX ports range from 0 to 65535. |
DL3012 | Multiple HEALTHCHECK instructions. |
DL3013 | Pin versions in pip. |
DL3014 | Use the -y switch. |
DL3015 | Avoid additional packages by specifying --no-install-recommends. |
DL3016 | Pin versions in npm . |
DL3017 | Do not use apk upgrade . |
DL3018 | Pin versions in apk add. Instead of apk add <package> use apk add <package>=<version> . |
DL3019 | Use the --no-cache switch to avoid the need to use --update and remove /var/cache/apk/* when done installing packages. |
DL3020 | Use COPY instead of ADD for files and folders. |
DL3021 | COPY with more than 2 arguments requires the last argument to end with / |
DL3022 | COPY --from should reference a previously defined FROM alias |
DL3023 | COPY --from cannot reference its own FROM alias |
DL3024 | FROM aliases (stage names) must be unique |
DL3025 | Use arguments JSON notation for CMD and ENTRYPOINT arguments |
DL3026 | Use only an allowed registry in the FROM image |
DL3027 | Do not use apt as it is meant to be a end-user tool, use apt-get or apt-cache instead |
DL3028 | Pin versions in gem install. Instead of gem install <gem> use gem install <gem>:<version> |
DL3029 | Do not use --platform flag with FROM. |
DL3030 | Use the -y switch to avoid manual input yum install -y <package> |
DL3031 | Do not use yum update |
DL3032 | yum clean all missing after yum command. |
DL3033 | Specify version with yum install -y <package>-<version> |
DL3034 | Non-interactive switch missing from zypper command: zypper install -y |
DL3035 | Do not use zypper update . |
DL3036 | zypper clean missing after zypper use. |
DL3037 | Specify version with zypper install -y <package>[=]<version> . |
DL3038 | Use the -y switch to avoid manual input dnf install -y <package> |
DL3039 | Do not use dnf update |
DL3040 | dnf clean all missing after dnf command. |
DL3041 | Specify version with dnf install -y <package>-<version> |
DL3042 | Avoid cache directory with pip install --no-cache-dir <package> . |
DL3043 | ONBUILD , FROM or MAINTAINER triggered from within ONBUILD instruction. |
DL3044 | Do not refer to an environment variable within the same ENV statement where it is defined. |
DL3045 | COPY to a relative destination without WORKDIR set. |
DL3046 | useradd without flag -l and high UID will result in excessively large Image. |
DL3047 | wget without flag --progress will result in excessively bloated build logs when downloading larger files. |
DL3048 | Invalid Label Key |
DL3049 | Label <label> is missing. |
DL3050 | Superfluous label(s) present. |
DL3051 | Label <label> is empty. |
DL3052 | Label <label> is not a valid URL. |
DL3053 | Label <label> is not a valid time format - must be conform to RFC3339. |
DL3054 | Label <label> is not a valid SPDX license identifier. |
DL3055 | Label <label> is not a valid git hash. |
DL3056 | Label <label> does not conform to semantic versioning. |
DL3057 | HEALTHCHECK instruction missing. |
DL3058 | Label <label> is not a valid email format - must be conform to RFC5322. |
DL3059 | Multiple consecutive RUN instructions. Consider consolidation. |
DL3060 | yarn cache clean missing after yarn install was run. |
DL4000 | MAINTAINER is deprecated. |
DL4001 | Either use Wget or Curl but not both. |
DL4003 | Multiple CMD instructions found. |
DL4004 | Multiple ENTRYPOINT instructions found. |
DL4005 | Use SHELL to change the default shell. |
DL4006 | Set the SHELL option -o pipefail before RUN with a pipe in it |
SC1000 | $ is not used specially and should therefore be escaped. |
SC1001 | This \c will be a regular 'c' in this context. |
SC1007 | Remove space after = if trying to assign a value (or for empty string, use var='' ... ). |
SC1010 | Use semicolon or linefeed before done (or quote to make it literal). |
SC1018 | This is a unicode non-breaking space. Delete it and retype as space. |
SC1035 | You need a space here |
SC1045 | It's not foo &; bar , just foo & bar . |
SC1065 | Trying to declare parameters? Don't. Use () and refer to params as $1 , $2 etc. |
SC1066 | Don't use $ on the left side of assignments. |
SC1068 | Don't put spaces around the = in assignments. |
SC1077 | For command expansion, the tick should slant left (` vs ´). |
SC1078 | Did you forget to close this double-quoted string? |
SC1079 | This is actually an end quote, but due to next char, it looks suspect. |
SC1081 | Scripts are case sensitive. Use if , not If . |
SC1083 | This {/} is literal. Check expression (missing ;/\n ?) or quote it. |
SC1086 | Don't use $ on the iterator name in for loops. |
SC1087 | Braces are required when expanding arrays, as in ${array[idx]} . |
SC1095 | You need a space or linefeed between the function name and body. |
SC1097 | Unexpected == . For assignment, use = . For comparison, use [ .. ] or [[ .. ]] . |
SC1098 | Quote/escape special characters when using eval , e.g. eval "a=(b)" . |
SC1099 | You need a space before the # . |
SC2002 | Useless cat. Consider cmd < file | .. or cmd file | .. instead. |
SC2015 | Note that A && B || C is not if-then-else. C may run when A is true. |
SC2026 | This word is outside of quotes. Did you intend to 'nest '"'single quotes'"' instead'? |
SC2028 | echo won't expand escape sequences. Consider printf . |
SC2035 | Use ./*glob* or -- *glob* so names with dashes won't become options. |
SC2039 | In POSIX sh, something is undefined. |
SC2046 | Quote this to prevent word splitting |
SC2086 | Double quote to prevent globbing and word splitting. |
SC2140 | Word is in the form "A"B"C" (B indicated). Did you mean "ABC" or "A\"B\"C" ? |
SC2154 | var is referenced but not assigned. |
SC2155 | Declare and assign separately to avoid masking return values. |
SC2164 | Use cd ... || exit in case cd fails. |
If you are an experienced Haskeller we would be really thankful if you would tear our code apart in a review.
-
Clone repository
git clone --recursive git@github.com:hadolint/hadolint.git
-
Install the dependencies
stack install
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"
Run unit tests.
stack test
Run integration tests.
./integration_test.sh
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.
- RedCoolBeans/dockerlint
- projectatomic/dockerfile_lint