Table of contents:

  1. Chain RUN instructions
  2. Example
  3. Instarctions

Chain RUN instructions

  • each RUN command will execute the command on top writable layer of the container, then commit the container as a new image
  • the new image is used for the next step in the Dockerfile. So each RUN instructions will create a new image layer
  • it is recommended to chain the RUN instructions in the Dockerfile to reduce the number of image layers it creates


Bellow we have a simple Dockerfile. We can modify the Dockerfile:

FROM debian:jessie
RUN apt-get update
RUN apt-get install -y git
RUN apt-get intall -y vim

instead of 4 lines we can agregate lines to get more cosins chain, like:

FROM debian:jessie
RUN apt-get update && apt-get install -y \
    git \

When building a docker image we have two steps instead of three:

Sending build context to Docker daemon  3.072kB
Step 1/2 : FROM debian:jessie
 ---> 3aaeab7a4777
Step 2/2 : RUN apt-get update && apt-get install -y 	git 	vim
 ---> Running in c628f9060664
Get:1 jessie/updates InRelease [44.9 kB]
Ign jessie InRelease
Get:2 jessie-updates InRelease [16.3 kB]
Get:3 jessie Release.gpg [1652 B]


Fundamental Instructions:

  • FROM
  • ARG

Configuration Instructions:

  • RUN
  • ADD
  • COPY
  • ENV

Execution Instructions:

  • CMD


  1. Docker
  2. Docker docs
  3. Getting started with Docker

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