如何查找容器已挂载的卷？Docker Compose中Prometheus服务/prometheus挂载来源排查

Great question! That unexpected /prometheus mount you're seeing in Portainer isn't a bug—it's actually a behavior baked into the official Prometheus Docker image. Here's how to track down all its details:

Why the Volume Exists (Even Without Defining It) #

The official prom/prometheus:latest image includes a VOLUME /prometheus directive in its Dockerfile. Docker automatically creates an anonymous volume for this path whenever you run the container, even if you don't explicitly define it in your docker-compose.yml. This volume stores Prometheus' time-series data, so it persists even if the container is recreated.

Step-by-Step to Find the Volume Details #

1. Use Docker CLI to Inspect the Container #

Run this command to get full details about your Prometheus container's mounts:

docker inspect <your-prometheus-container-name-or-id>

Look for the Mounts section in the output. It will show:

• Type: Should be volume (anonymous volume)
• Name: A random alphanumeric ID assigned to the anonymous volume
• Source: The actual path on your host machine (usually something like /var/lib/docker/volumes/<volume-id>/_data)
• Destination: /prometheus (the path inside the container)

2. Check Portainer's Volumes Page #

Portainer makes this even easier:

• Navigate to the Volumes tab in Portainer
• Use the search or filter to find volumes associated with your Prometheus container (look for the container name in the "Used By" column)
• Click on the volume to view its details, including the host path and which containers it's mounted to

3. Verify the Compose Configuration #

To see the full, expanded configuration Docker Compose uses (including the implicit volume), run:

docker compose config

You'll notice the /prometheus volume is automatically added under the volumes section of your Prometheus service.

Why You Might Not See the Folder #

• On the host: The path /var/lib/docker/volumes/... is owned by the root user, so you'll need to use sudo to list or access it (e.g., sudo ls /var/lib/docker/volumes/<volume-id>/_data).
• In the container: The /prometheus folder definitely exists inside the container—try running docker exec -it <container-id> ls /prometheus to confirm it (you might need sudo here too if the container runs as a non-root user).

内容的提问来源于stack exchange，提问作者Eugen Konkov