Create a base imageEstimated reading time: 3 minutes
Most Dockerfiles start from a parent image. If you need to completely control the contents of your image, you might need to create a base image instead. Here’s the difference:
A parent image is the image that your image is based on. It refers to the contents of the
FROMdirective in the Dockerfile. Each subsequent declaration in the Dockerfile modifies this parent image. Most Dockerfiles start from a parent image, rather than a base image. However, the terms are sometimes used interchangeably.
A base image either has no
FROMline in its Dockerfile, or has
This topic shows you several ways to create a base image. The specific process will depend heavily on the Linux distribution you want to package. We have some examples below, and you are encouraged to submit pull requests to contribute new ones.
Create a full image using tar
In general, you’ll want to start with a working machine that is running the distribution you’d like to package as a parent image, though that is not required for some tools like Debian’s Debootstrap, which you can also use to build Ubuntu images.
It can be as simple as this to create an Ubuntu parent image:
$ sudo debootstrap xenial xenial > /dev/null $ sudo tar -C xenial -c . | docker import - xenial a29c15f1bf7a $ docker run xenial cat /etc/lsb-release DISTRIB_ID=Ubuntu DISTRIB_RELEASE=16.04 DISTRIB_CODENAME=xenial DISTRIB_DESCRIPTION="Ubuntu 16.04 LTS"
There are more example scripts for creating parent images in the Docker GitHub Repo:
- CentOS / Scientific Linux CERN (SLC) on Debian/Ubuntu or on CentOS/RHEL/SLC/etc.
- Debian / Ubuntu
Creating a simple parent image using scratch
You can use Docker’s reserved, minimal image,
scratch, as a starting point for building containers. Using the
scratch “image” signals to the build process that you want the next command in the
Dockerfile to be the first filesystem layer in your image.
scratch appears in Docker’s repository on the hub, you can’t pull it, run it, or tag any image with the name
scratch. Instead, you can refer to it in your
Dockerfile. For example, to create a minimal container using
FROM scratch ADD hello / CMD ["/hello"]
Assuming you built the “hello” executable example from the Docker GitHub example C-source code, and you compiled it with the
-static flag, you can then build this Docker image using:
docker build --tag hello .
NOTE: Because Docker for Mac and Docker for Windows use a Linux VM, you must compile this code using a Linux toolchain to end up with a Linux binary. Not to worry, you can quickly pull down a Linux image and a build environment and build within it:
$ docker run --rm -it -v $PWD:/build ubuntu:16.04 container# apt-get update && apt-get install build-essential container# cd /build container# gcc -o hello -static -nostartfiles hello.c
Then you can run it (on Linux, Mac, or Windows) using:
docker run --rm hello
This example creates the hello-world image used in the tutorials. If you want to test it out, you can clone the image repo.
There are lots more resources available to help you write your
- There’s a complete guide to all the instructions available for use in a
Dockerfilein the reference section.
- To help you write a clear, readable, maintainable
Dockerfile, we’ve also written a
Dockerfilebest practices guide.
- If your goal is to create a new Official Repository, be sure to read up on Docker’s Official Repositories.