Docker container runs CMD command three different ways, why?

Question

I have set up my Dockerfile, it looks like this:

FROM python:3.6
ARG label
ARG seeds
ARG dataset_name=${label}_terms

RUN mkdir /prodigy
WORKDIR /prodigy
COPY ./prodigy-1.8.1-cp35.cp36.cp37-cp35m.cp36m.cp37m-linux_x86_64.whl /prodigy

RUN pip install prodigy-1.8.1-cp35.cp36.cp37-cp35m.cp36m.cp37m-linux_x86_64.whl
RUN pip install -U spacy
RUN python -m spacy download en_core_web_lg

EXPOSE 8080

RUN mkdir /work
ENV PRODIGY_HOME /work
WORKDIR /work
COPY ./prodigy.json /work

RUN prodigy dataset ${dataset_name}

ENV LABEL=${label}
ENV SEEDS=${seeds}

CMD prodigy terms.teach ${LABEL}_terms en_core_web_lg --seed "$SEEDS"

It works, but not as expected. It should run CMD command just once. Instead it does it 3 different ways (ps aux output):

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.0   4280   692 ?        Ss   08:47   0:00 /bin/sh -c prodigy terms.teach ${LABEL}_terms en_core_web_lg --seed "$SEEDS"
root         8  0.0  0.0   4280   740 ?        S    08:47   0:00 /bin/sh /usr/local/bin/prodigy terms.teach TRANSFER_terms en_core_web_lg --seed transfer, relocation, relegation
root         9 46.1 13.7 2329976 1687016 ?     Sl   08:47  15:13 python -m prodigy terms.teach TRANSFER_terms en_core_web_lg --seed transfer, relocation, relegation

I wonder what is this a standard behavior? How can i make my Dockerfile clean?

Answer 1

(Without looking into the details of the command you're running) I suspect that the prodigy command itself spawns a new shell / subcommands.

From the list of processes, PID 1 is the process that's run by Docker as the container's main process; the other processes are child-processes of the first one, and started by the main process.