Host Metrics with the Container Agent

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Disk check

The Disk check reports host metrics with the container Agent for any storage mounted on the host and exposed to the container as a volume. No additional setup is required.

Metrics for partitions

The layered nature of Linux storage (block devices, logical volumes, and partitions) makes it necessary to have a partition mounted to report its free space.

The container Agent reports disk metrics and rates for every wholly or partially accessible partition. Cgroups and Docker enforce this separation. To allow disk usage reporting on a partition, you need to expose it through a Docker volume with the -v argument to docker run. The following options are available:

Create a dummy file in the filesystem to watch and expose it through Docker. The Agent can’t access any other file on this partition.
```
-v /mnt/loop/dummyfile:/host/loop0:ro
```
Expose the whole mount-point as read-only. The Agent can access the folder hierarchy and world-readable files.
```
-v /mnt/loop:/host/loop0:ro
```
If the mount path is unknown (dynamically mounted volumes), but the parent directory is constant, expose the parent folder. The Agent is able to access all volumes mounted in this folder’s children.
```
-v /mnt/:/host/mnt:ro
```

Troubleshooting

Missing disk metrics

If you customized the Docker image or mount a custom directory to the Agent’s conf.d folder, do one of the following for the Disk check:

Make sure the default conf.yaml is present.
Enable a customized conf.yaml.
Disable the check.

Permission denied errors

You may see permission denied errors with the containerized Agent when collecting disk metrics from certain virtual mount points. This usually occurs when the host’s entire root filesystem is exposed to the container. The Agent finds shm or netns mount points, which cannot generate metrics.

Here is an example of a related log reported by the Agent:

10:12:52 PST | WARN | (datadog_agent.go:149 in LogMessage) | (disk.py:114) | Unable to get disk metrics for /run/docker/netns/9ec58235910c: [Errno 13] Permission denied: '/run/docker/netns/9ec58235910c'

Ideally, you should only expose useful paths to the Agent’s container. If needed, prevent these logs from being reported by the Agent by updating the Disk check’s conf.yaml to exclude the relevant file systems by using one of the following parameters: