So here’s a permanent fix that works for systemd (Ubuntu 15.04 and higher):

1. create a new file /etc/systemd/system/docker.service.d/overlay.conf with the following content:

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

2. flush changes by executing:

sudo systemctl daemon-reload

3. verify that the configuration has been loaded:

systemctl show --property=ExecStart docker

4. restart docker:

sudo systemctl restart docker