如何在Docker镜像/容器上专门执行Docker容器的内置Shell Docker

Question

thank you for reading my post.

Problem:

# docker ps
CONTAINER ID        IMAGE                  COMMAND             
35c8b832403a        ubuntu1604:1   "sh -c /bin/sh"    

# docker exec -i -t 35c8b832403a type type
rpc error: code = 2 desc = oci runtime error: exec failed: container_linux.go:262: starting container process caused "exec: \"type\": executable file not found in $PATH"

# Dockerfile
FROM ubuntu:16.04

ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
RUN apt-get update && apt-get -y upgrade
ENTRYPOINT ["sh", "-c"]
CMD ["/bin/bash"]

Description:

My objective is to get "type" shell builtin been execute in a way of writing docker exec as below

docker exec -i -t 35c8b832403a type type (FAILED)

NOT

docker exec -i -t 35c8b832403a sh -c "type type" (PASSED)

I have googling around, do some modification in the container (change /etc/profile, /etc/environment, bashrc) but failed.

From the docker documentation itself, it has state that:

COMMAND will run in the default directory of the container. It the underlying image has a custom directory specified with the WORKDIR directive in its Dockerfile, this will be used instead.

COMMAND should be an executable, a chained or a quoted command will not work. Example: docker exec -ti my_container "echo a && echo b" will not work, but docker exec -ti my_container sh -c "echo a && echo b" will.

But seem it IS POSSIBLE when I able to get the right output FROM DOCKER FEDORA (Dockerfile: FROM fedora:25)

# docker ps
CONTAINER ID        IMAGE                  COMMAND             
2a17b2338518        fedora25:1   "sh -c /bin/sh" 

# docker exec -i -t 2a17b2338518 type type
type is a shell builtin

Question:

Is there any way to enable this on Ubuntu docker? Image/Container tweaks? Vagrantfile Configuration? Please help.

Others:

Using docker run, I able to get the right output because of the "ENTRYPOINT" in the Dockerfile. However the image need to be save instead of export .

Answer 1

CMD and ENTRYPOINT are meaningless if you run docker exec . The remaining arguments are taken as the command and executed inside the already existing container.

Maybe you wanted to use docker run ?

Answer 2

Just in case, to be able to execute type as you expect, it would need to be part of the path. Being a shell builtin wouldn't help because as you said, you don't want to execute /bin/bash -c 'type type'

If you want to have type executed as a builtin shell command, this means you need to execute a shell /bin/bash or /bin/sh and then execute 'type type' on it, making it /bin/bash -c 'type type'

After all, as @Henry said, docker exec is a the full command that will be executed and there is no place for CMD or ENTRYPOINT on it.