Default Docker entrypoint

Question

I am creating an image from another image that set a specific entrypoint. However I want my image to have default one. How do I reset the ENTRYPOINT?

I tried the following Dockerfile:

FROM some-image
ENTRYPOINT ["/bin/sh", "-c"]

Unfortunately it doesn't work like the default entrypoint as it need the command to be quoted.

docker run myimage ls -l /    # "-l /" arguments are ignored
file1 file2 file3             # files in current working directory

docker run myimage "ls -l /"  # works correctly

How do I use commands without quoting?

Answer 1

This isn't really related to docker. Try running the following:

/bin/sh -c echo foo

/bin/sh -c "echo foo"

The -c means that /bin/sh only picks up one argument. So removing the -c from the entrypoint you define should fix it. This is more flexible than resetting the entry point; e.g. you can do this to use Software Collections:

ENTRYPOINT ["scl", "enable", "devtoolset-4", "--", "bash"]

Answer 2

To disable an existing ENTRYPOINT, set an empty array in your docker file

ENTRYPOINT []

Then your arguments to docker run will exec as normal.

The reason your ENTRYPOINT ["/bin/sh", "-c"] requires quoted strings is that without the quotes, the arguments to ls are being passed to sh instead.

Unquoted results in lots of arguments being sent to sh

"/bin/sh", "-c", "ls", "-l", "/"

Quoting allows the complete command (sh -c) to be passed on to sh as one argument.

"/bin/sh", "-c", "ls -l /"