docker logs doesn't log detached exec

Question

My Dockerfile is

FROM node:4

RUN npm install -g yarn

WORKDIR /app

I run docker run -d and mount my current working directory as a volume. All the deps are installed by yarn. I have a npm script to lint the files.

If I do docker exec -it [container] npm run lint it works as expected and I can see all the logs. But if I do docker exec -itd [container] npm run lint, it exits immediately which is expected. But I can't see the logs by running docker logs [container]. How do I reattach the exec or just see to the logs?

I tried docker attach [container] it goes to the repl of nodejs. Why is that?

Answer 1

As mentioned in "Docker look at the log of an exited container", you can use docker logs

docker logs -t <container>

That will show stdout/stderr (with timestamps because of the -t option).

For that last 50 lines of those logs:

docker logs -t <container id> | tail -n 50

Note: that would work only if npm run lint is run by your container (docker run <image> npm run lint)

If your docker exec exits immediately, then yes, there would be no logs produces by the container itself.