found solution
First create directory and file for custom configuration:
sudo mkdir -p /etc/systemd/system/docker.service.d sudo $EDITOR /etc/systemd/system/docker.service.d/docker-storage.conf
For docker version before 17.06-ce paste:
[Service] ExecStart= ExecStart=/usr/bin/docker daemon -H fd:// --graph="/mnt"
For docker after 17.06-ce paste:
[Service] ExecStart= ExecStart=/usr/bin/dockerd -H fd:// --data-root="/mnt"
Alternative method through daemon.json
I recently tried above procedure with 17.09-ce on Fedora 25 and it seem to not work. Instead of that simple modification in /etc/docker/daemon.json do the trick:
{ "graph": "/mnt", "storage-driver": "overlay" }
Despite the method you have to reload configuration and restart Docker:
sudo systemctl daemon-reload sudo systemctl restart docker
To confirm that Docker was reconfigured:
docker info|grep "loop file"
In recent version (17.03) different command is required:
docker info|grep "Docker Root Dir"
Output should look like this:
Data loop file: /mnt/devicemapper/devicemapper/data Metadata loop file: /mnt/devicemapper/devicemapper/metadata
Or:
Docker Root Dir: /mnt
Then you can safely remove old Docker storage:
rm -rf /var/lib/docker