Dockerfile - CMD does not run the shell script

Question

Ok just learning about creating a Dockerfile and my understanding (which is probably wrong) is that the CMD command should be able to run a shell script from within the container once it is placed there.

I am just trying it out with a vanilla apache2 install

Dockerfile

FROM ubuntu:latest

ADD install-apache.sh /Scripts/install-apache.sh
RUN chmod +x /Scripts/install-apache.sh
CMD [/Scripts/install-apache.sh]



RUN echo "Hope this worked!"

I have also tried this:

CMD ["/Scripts/install-apache.sh"]

When I use the RUN command it works (without the [ and ])

So I am a bit lost what the CMD is suppose to do.

I followed the instructions from http://kimh.github.io and read through the docker docs as well.

Question: How am I using the CMD wrong and how should I use it in this scenario?

Sebastian · Accepted Answer · 2017-01-28 21:03:11Z

5

RUN is executed while you are building an image. This is usually used to install things or perform modifications in the resulting image.
CMD is executed when the container is started. Use this to e.g. start applications.

Also check the docs

The main purpose of a CMD is to provide defaults for an executing container. These defaults can include an executable, or they can omit the executable, in which case you must specify an ENTRYPOINT instruction as well.

answered Jan 28, 2017 at 21:03

Sebastian

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5 Comments

jwknz Over a year ago

Oh so the CMD is run when a user runs the container I am building - and RUN is used when I am building it?

Sebastian Over a year ago

@JeffKranenburg exactly

jwknz Over a year ago

Thanks @Sebastian - will accept in a few minutes when SO allows me too :-)

mkasberg Over a year ago

Yep. You could literally just change CMD [/Scripts/install-apache.sh] to RUN /Scripts/install-apache.sh and it would do what you're expecting it to. As an example of CMD, you'd likely want something like CMD ["httpd", "-DFOREGROUND"] to automatically start apache for you when the container boots up.

Beginner Over a year ago

But i want to run the .sh file on CMD how can i achieve that ?

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