docker stats shows zero memory usage even for running containers

I have two containers ran by Docker Swarm:

# docker ps
CONTAINER ID        IMAGE                               COMMAND                  CREATED             STATUS              PORTS               NAMES
18f1e7d79f5b        default/image1:latest               "/bin/sh -c 'java ..."   12 hours ago        Up 12 hours                             image1.1.x56zz152kmqtqpxzle5nkbs8r
11d1f05fcff1        default/image2:latest               "java -cp /app/sca..."   13 hours ago        Up 13 hours                             image2.1.ljztzeeh8i5r6ebr3n4hcj45e

$ docker stats --no-stream
CONTAINER           CPU %               MEM USAGE / LIMIT   MEM %               NET I/O             BLOCK I/O           PIDS
18f1e7d79f5b        0.92%               0B / 0B             0.00%               648B / 0B           0B / 0B             0
11d1f05fcff1        0.91%               0B / 0B             0.00%               39.9MB / 26.9MB     51.2MB / 0B         0

Host OS is Debian Jessie. There are JVM applications in both containers. Why does docker stats show zero memory usage? Should I configure my Java apps somehow to be able to see memory usage in docker stats? Is there some other way to check memory usage?

Answer

It is quite possible that memory cgroup accounting is not enabled in your kernel (which is a common problem that others have hit as well over time on Debian/Ubuntu based installs).

Can you verify with docker info or the output from the daemon that you aren’t seeing messages like the following, nicely summarized in this blog post: Debian Jessie w/Docker? If so, the fix is also listed there, as well as in the GitHub issue I linked in the first sentence. There is also a section in the install documentation about enabling cgroup memory accounting although it only mentions Ubuntu and not Debian.