dockerfile: how use CMD or ENTRYPOINT from base image

docker dockerfile docker-build
Dave C picture Dave C · Apr 5, 2017 · Viewed 11.9k times · Source

I have several base docker images which are not owned by me (so I cannot modify them). However, I'm creating new images from them with additional things installed.

What I can't figure out is how to tell dockerfile to copy the CMD (or ENTRYPOINT) of the base image. Something like this:

FROM other:latest
RUN my-extra-install
CMD <use-the-CMD-from-base-image>

I don't think there's any direct syntax for the CMD command to do what I want. I'm wondering if there's a workaround.

Answer

Vor picture Vor · Apr 5, 2017

If you left it blank in your new Dockerfile, it will inherit the one from the base image.

For example:

base

FROM ubuntu
CMD ["echo", "AAA"]

layer1

FROM base

If you build above images and run layer1 you will get the following:

$ sudo docker run -it layer1
AAA

Related questions

Docker: unable to prepare context: unable to evaluate symlinks in Dockerfile path: GetFileAttributesEx

I just downloaded Docker Toolbox for Windows 10 64bit today. I'm going through the tutorial. I'm receving the following error when trying to build an image using a Dockerfile. Steps: Launched Docker Quickstart terminal. testdocker after creating it. Prepare Dockerfile as …

Read More
Docker container doesn't expose ports when --net=host is mentioned in the docker run command

I have a CentOS docker container on a CentOS docker host. When I use this command to run the docker image docker run -d --net=host -p 8777:8777 ceilometer:1.x the docker container get host's IP but doesn't have ports assigned …

Read More
Docker build command with --tag unable to tag images

I have trying to build a Docker image using a Dockerfile available locally. docker build -t newimage . I have used this command multiple times earlier too, but somehow its not working currently and i am stuck finding the reason for …

Read More