Getting rid of duplicated journalctl logs

[4JX]

I'm guessing this is a byproduct of how nixos itself handles containers by assigning them to systemd units, but ever since I switched backends* from podman to docker I've been having this annoying issue where practically every log line is printed both by the container and the service managing it:

*I don't recall it being the case with podman, but I'm not 100% sure.

Is there a way to disable one of the two log streams? Preferably the systemd unit one, as that doesn't seem to preserve color.

[aksiksi]

compose2nix sets the log-driver to journald on each OCI container. This results in a --log-driver flag being passed to the docker run ... command executed by the OCI container systemd service. One of these logs is definitely due to this flag.

For Docker specifically, you can also configure a log driver at the daemon/engine level (ref). This is controlled by the virtualisation.docker.logDriver setting, which defaults to journald. Could you try setting this log driver to none?

[4JX]

Apologies for the delay in answering.

I'd already tried virtualisation.docker.logDriver = "none" but that had no effect. Setting the service specific config to json-file or none eliminates the "container" logs and keeps the *-start service ones.

[aksiksi]

I think I see what the problem is.

For Podman, the container runs in detached mode, which means container output does not go to stdout: https://github.com/NixOS/nixpkgs/blob/b47fd6fa00c6afca88b8ee46cfdb00e104f50bca/nixos/modules/virtualisation/oci-containers.nix#L335

I guess this can only be done with Podman because it is natively integrated with systemd. That is, systemd events will propagate to Podman and vice-versa.

I would recommend filing an upstream issue to ask about this, and whether it would be possible to add an option to suppress stdout in favor of the log-driver setting. One idea could be to disable stdout logging for Docker if log-driver == "journald".

For now, your only option is to disable logging at the service level.