Back in March I wrote about Using Overlay file system with Docker on Ubuntu – those instructions applied to Ubuntu before the switch to systemd e.g. 14.04 and earlier.

The move to systemd means that changes to /etc/default/docker don’t have any effect any more.

To get systemd to dance along to our tune needs a file like this:

/etc/systemd/system/docker.service.d/overlay.conf

[Service]
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// --storage-driver=overlay

To make this work use the following script (or get it from gist to avoid silly copy/past replacement of < with &lt;):

sudo mkdir /etc/systemd/system/docker.service.d
sudo bash -c 'cat <<EOF > /etc/systemd/system/docker.service.d/overlay.conf
[Service]
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// --storage-driver=overlay
EOF'
sudo systemctl daemon-reload
sudo systemctl restart docker

Now when you run ‘sudo docker info’ you should see something like:

...
Storage Driver: overlay
 Backing Filesystem: extfs
...

At least you didn’t need to upgrade the kernel this time – small mercies.

NB this is somewhat (inaccurately right now) documented in Control and configure Docker with systemd – I can feel a PR coming on.