why docker logs doesn't show any log using your dockerfile

[kundeng]

Hi, I tested the dockerfile for debian 8. For some reason, the docker logs -f containername doesn't show anything. Do you know why?

[j8r]

That's normal, systemd logs by default to journal and stored as a binary log format. I've tried to log to stdout/console with --log-target=console or --default-standard-output=journal+console, but the problem is known and not yet fixed by moby.

We can get around by executing systemd with a shell and redirect to stdout, but that's ugly. Furthermore, we will not be able to have logs inside the container with journalctl.

[kundeng]

You mean you tried multiple methods but it didn't work?

Your get-around is something like this: CMD ["/bin/bash", "-c", "exec /sbin/init --log-target=journal 3>&1"]

[j8r]

Yes @kundeng that was exaclty what I was thinking for (apart changing bash by sh).

I've seen this initially on https://github.com/solita/docker-systemd/blob/a56a659e099f607df006f6ed89ebb99332ebdab9/Dockerfile#L27.

Thanks to have reported the issue by the way! I will try other options before opting for this one.

[j8r]

This last command fix only for logs of the boot sequence. When we docker exec on the container, the commands aren't logged.

Even https://github.com/solita/docker-systemd doesn't do it, and recommend using docker exec systemd journalctl to show system logs.

I won't add this fix because the boot sequence's logs are not really useful, and I haven't found a way to centralize all logs to docker logs.

OpenRC have also the same problem. I would like to keep the overall simple - just have containers to test if a service works or not.