How to generate a Dockerfile from an image

Question

Is it possible to generate a Dockerfile from an image   I want to know for two reasons    I can download images from the repository but would like to see the recipe that generated them  I like the idea of saving snapshots  but once I am done it would be nice to have a structured format to review what was done

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Update Dec 2018 to BMW s answer chenzj dfimage - as described on hub docker com regenerates Dockerfile from other images  So you can use it as follows  docker pull chenzj dfimage alias dfimage  quot docker run -v  var run docker sock  var run docker sock --rm chenzj dfimage quot  dfimage IMAGE ID  gt  Dockerfile

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How to generate or reverse a Dockerfile from an image   You can  alias dfimage  quot docker run -v  var run docker sock  var run docker sock --rm alpine dfimage quot  dfimage -sV 1 36 nginx latest  It will pull the target docker image automaticlaly and export Dockerfile  Parameter -sV 1 36 is not always required  Reference  https   hub docker com repository docker alpine dfimage below is the old answer  it doesn t work any more    docker pull centurylink dockerfile-from-image   alias dfimage  quot docker run -v  var run docker sock  var run docker sock --rm centurylink dockerfile-from-image quot    dfimage --help Usage  dockerfile-from-image rb  options   lt image id gt      -f  --full-tree                  Generate Dockerfile for all parent layers     -h  --help                       Show this message

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x000D   x000D  docker pull chenzj dfimage   alias dfimage  docker run -v  var run docker sock  var run docker sock --rm chenzj dfimage   dfimage image id x000D   x000D   x000D   Below is ouput of dfimage command    dfimage 0f1947a021ce  FROM node 8 WORKDIR  usr src app  COPY file e76d2e84545dedbe901b7b7b0c8d2c9733baa07cc821054efec48f623e29218c in    RUN  bin sh -c npm install COPY dir a89a4894689a38cbf3895fdc0870878272bb9e09268149a87a6974a274b2184a in    EXPOSE 8080 CMD   quot npm quot   quot start quot

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It is not possible at this point  unless the author of the image explicitly included the Dockerfile    However  it is definitely something useful  There are two things that will help to obtain this feature    Trusted builds  detailed in this docker-dev discussion More detailed metadata in the successive images produced by the build process  In the long run  the metadata should indicate which build command produced the image  which means that it will be possible to reconstruct the Dockerfile from a sequence of images

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A bash solution    docker history --no-trunc  argv    tac   tr -s       cut -d     -f 5-   sed  s   bin sh -c   nop    g    sed  s   bin sh -c RUN g    sed  s   amp  amp    n   amp   g    sed  s  s  0-9        0-9   s  kMG  B s    g    head -n -1   Step by step explanations   tac   reverse the file tr -s                                           trim multiple whitespaces into 1 cut -d     -f 5-                                remove the first fields  until X months years ago  sed  s   bin sh -c   nop    g                   remove  bin sh calls for ENV LABEL    sed  s   bin sh -c RUN g                        remove  bin sh calls for RUN sed  s   amp  amp    n   amp   g                            pretty print multi command lines following Docker best practices sed  s  s  0-9        0-9   s  kMG  B s    g       remove layer size information head -n -1                                      remove last line   SIZE COMMENT  in this case    Example        dih ubuntu 18 04 ADD file 28c0771e44ff530dba3f237024acc38e8ec9293d60f0e44c8c78536c12f13a0b in   RUN set -xe     amp  amp   echo     bin sh   gt   usr sbin policy-rc d     amp  amp   echo  exit 101   gt  gt   usr sbin policy-rc d     amp  amp   chmod  x  usr sbin policy-rc d     amp  amp   dpkg-divert --local --rename --add  sbin initctl     amp  amp   cp -a  usr sbin policy-rc d  sbin initctl     amp  amp   sed -i  s  exit   exit 0    sbin initctl     amp  amp   echo  force-unsafe-io   gt   etc dpkg dpkg cfg d docker-apt-speedup     amp  amp   echo  DPkg  Post-Invoke    rm -f  var cache apt archives   deb  var cache apt archives partial   deb  var cache apt   bin    true        gt   etc apt apt conf d docker-clean     amp  amp   echo  APT  Update  Post-Invoke    rm -f  var cache apt archives   deb  var cache apt archives partial   deb  var cache apt   bin    true        gt  gt   etc apt apt conf d docker-clean     amp  amp   echo  Dir  Cache  pkgcache     Dir  Cache  srcpkgcache       gt  gt   etc apt apt conf d docker-clean     amp  amp   echo  Acquire  Languages  none     gt   etc apt apt conf d docker-no-languages     amp  amp   echo  Acquire  GzipIndexes  true   Acquire  CompressionTypes  Order    gz     gt   etc apt apt conf d docker-gzip-indexes     amp  amp   echo  Apt  AutoRemove  SuggestsImportant  false     gt   etc apt apt conf d docker-autoremove-suggests RUN rm -rf  var lib apt lists   RUN sed -i  s    s   deb  universe     1 g   etc apt sources list RUN mkdir -p  run systemd     amp  amp   echo  docker   gt   run systemd container CMD    bin bash

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I somehow absolutely missed the actual command in the accepted answer  so here it is again  bit more visible in its own paragraph  to see how many people are like me    docker history --no-trunc  lt IMAGE ID gt

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This is derived from  fallino s answer  with some adjustments and simplifications by using the output format option for docker history  Since macOS and Gnu Linux have different command-line utilities  a different version is necessary for Mac  If you only need one or the other  you can just use those lines      bin bash case   OSTYPE  in     linux           docker history --no-trunc --format     CreatedBy     1     extract information from layers         tac                                                        reverse the file         sed  s     3       bin   ba    sh -c RUN                   change  bin  ba  sh calls to RUN         sed  s  RUN   nop                                          remove RUN   nop  calls for ENV LABEL            sed  s     amp  amp         n   amp   amp   g                              pretty print multi command lines following Docker best practices            darwin           docker history --no-trunc --format     CreatedBy     1     extract information from layers         tail -r                                                    reverse the file         sed -E  s     3     bin  ba  sh -c RUN                     change  bin  ba  sh calls to RUN         sed  s  RUN   nop                                          remove RUN   nop  calls for ENV LABEL            sed   s     amp  amp             n   amp   amp   g                         pretty print multi command lines following Docker best practices                       echo  unknown OSTYPE   OSTYPE         esac

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To understand how a docker image was built  use the docker history --no-trunc command   You can build a docker file from an image  but it will not contain everything you would want to fully understand how the image was generated   Reasonably what you can extract is the MAINTAINER  ENV  EXPOSE  VOLUME  WORKDIR  ENTRYPOINT  CMD  and ONBUILD parts of the dockerfile   The following script should work for you      bin bash docker history --no-trunc   1      sed -n -e  s    bin sh -c   nop    MAINTAINER           0 B  1 p      head -1 docker inspect --format    range  e     Config Env   ENV    e     end    range  e  v     Config ExposedPorts   EXPOSE    e     end    range  e  v     Config Volumes   VOLUME    e     end    with  Config User  USER        end     with  Config WorkingDir  WORKDIR        end     with  Config Entrypoint  ENTRYPOINT   json      end     with  Config Cmd  CMD   json      end     with  Config OnBuild  ONBUILD   json      end      1    I use this as part of a script to rebuild running containers as images   https   github com docbill docker-scripts blob master docker-rebase  The Dockerfile is mainly useful if you want to be able to repackage an image   The thing to keep in mind  is a docker image can actually just be the tar backup of a real or virtual machine    I have made several docker images this way  Even the build history shows me importing a huge tar file as the first step in creating the image

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