Notes - Changing the default Docker root directory

TIL you can change the default root dir for Docker. This is fucking rad.

I learned this watching this Raid Owl video about using Docker on a GL.iNet Slate 7 travel router.

The reason to do this is for devices with limited / storage and want to save the docker images and any unmapped volumes to a different location. Think the Lenovo 110S. This only has a 32GB eMMC flash drive for /. But it has a NVMe slot. We can change the Docker root dir to a dir on the NVMe and give a lot more breathing room.

New dir

First we need to make a new location. This folder has to be called docker.

sudo mkdir /mnt/test/docker

It is critical the final folder in the chain is named docker.

Set path

We are going to create a file in /etc/docker called daemon.json.

sudo nano /etc/docker/daemon.json

Now add this:

{
 "data-root": "/new/path/docker"
}

Now restart Docker:

sudo systemctl restart docker

We can verify the new path with:

docker info | grep "Docker Root Dir"

We can also pull an image and then verify where it is stored:

docker pull nginx

docker image inspect ngnix

In the inspect we can see the location for the image under the "Data" section.