I have a very simple Dockerfile that I’m using as an example of layers.
$ cat Dockerfile
FROM ubuntu
RUN echo "layer 1" >> /layers
RUN echo "layer 2" >> /layers
RUN echo "layer 3" >> /layers
RUN echo "layer 4" >> /layers
ENTRYPOINT cat /layers
I’ve built it. Now if I run it…
$ docker run --rm layer-example
layer 1
layer 2
layer 3
layer 4
But what if I don’t want to use that entrypoint? I can override the entyrpoint and then provide another command.
docker run --entrypoint "/usr/bin/env" --name layer-example layer-example /bin/bash -c 'while true; do echo sleeping; sleep 2; done'
Note that I’m using env as the entrypoint, and then the actual command I want ot run is /bin/bash -c 'while true; do echo sleeping; sleep 2; done'.
Interestingly env just forwards the command on and runs it.
$ /usr/bin/env echo hi
hi
If I run it:
$ docker run --entrypoint "/usr/bin/env" --name layer-example layer-example /bin/bash -c 'while true; do echo sleeping; sleep 2; done'
sleeping
sleeping
sleeping
sleeping
sleeping
...
In another terminal I stop and remove the container via:
docker rm -f layer-example