I don't believe there is log rotation enabled in unraid's implementation of docker. There doesn't seem to be a limit on log size either.   I kept running out of space in my docker image and finally realized that a few of the containers were filling up the image with their logs. One container had a log that was 2.8GB (couchpotato)   The temporary solution was to reinstall the container and it reset the files in /var/lib/docker/containers and got rid of the large logs. It freed up a ton of s