Description

Hey all! I Recently found an odd bug with the Docker Daemon through my adventures of hardening a container. I want to modify the values for ulimit via the daemon.json file in accordance with the CIS_Docker 1.12 benchmark, and I quickly referred to the docker docs, however it seems through my search, I came up empty on a documented way to do this. I attempted to follow #25566 as a guide, however values that I input to the "default-ulimits" field return errors, and thus the docker daemon is unable to be started.

Steps to reproduce the issue:

1. If it's not already available, create the following file:

/etc/docker/daemon.json

2. Add in the following line:

{"default-ulimits": {"nofile":"100:200"}}

3. Restart the Docker daemon.

Describe the results you received:
level=fatal msg="unable to configure the Docker daemon with file /etc/docker/daemon.json: the following directives don't match any configuration option: nofile\n"

Describe the results you expected:
Docker daemon should be able to start, and pass the --default-ulimit as an argument with the respective ulimits.

Additional information you deem important (e.g. issue happens only occasionally):
This runs cleanly through the command line for just nproc, and same for nofile:

dockerd --default-ulimit nproc=1024:2408 --default-ulimit nofile=100:200

Output of docker version:

Docker version 1.12.3, build 6b644ec

Additional environment details (AWS, VirtualBox, physical, etc.):
AWS

Extra: In the case that it's not a bug and simply lack of documentation, I would be more than willing to help document the use cases for ulimit, as currently there are no examples of modifying ulimit within daemon.json.

Thanks in advance!