How to override the CMD command in the docker run line

Question

How you can replace the cdm based on the docker documentation: https://docs.docker.com/reference/builder/#cmd

You can override the CMD command

Dockerfile:

RUN chmod +x /srv/www/bin/* & chmod -R 755 /srv/www/app
RUN pip3 install -r /srv/www/app/pip-requirements.txt
EXPOSE 80
CMD ["/srv/www/bin/gunicorn.sh"]

the docker run command is:

docker run --name test test/test-backend

I tried

docker run --name test test --cmd ["/srv/www/bin/gunicorn.sh"]
docker run --name test test cmd ["/srv/www/bin/gunicorn.sh"]

But the console say this error:

System error: exec: "cmd": executable file not found in $PATH

Solution 1

The right way to do it is deleting cmd ["..."]

 docker run --name test test/test-backend /srv/www/bin/gunicorn.sh

Solution 2

The Dockerfile uses CMD instruction which allows defaults for the container being executed.

The below line will execute the script /srv/www/bin/gunicorn.sh as its already provide in CMD instruction in your Dockerfile as a default value, which internally gets executed as /bin/sh -c /srv/www/bin/gunicorn.sh during runtime.

 docker run --name test test/test-backend 

Now say if you want to run some thing else, just add that at a end of the docker run. Now below line should run bash instead.

docker run --name test test/test-backend /bin/bash

Ref: Dockerfile Best Practices

Solution 3

For those using docker-compose:

docker-compose run [your-service-name-here-from-docker-compose.yml] /srv/www/bin/gunicorn.sh

In my case I'm reusing the same docker service to run the development and production builds of my react application:

docker-compose run my-react-app npm run build

Will run my webpack.config.production.js and build the application to the dist. But yes, to the original question, you can override the CMD in the CLI.