原因
Docker API更新导致Portainer无法链接local环境，提示Environment local is unreachable。

解决方法
This worked for me. I'm using CE version.

nano /lib/systemd/system/docker.service

Add this line into [Service]

### Anything between here and the comment below will become the contents of the drop-in file

[Service]
Environment=DOCKER_MIN_API_VERSION=1.24

### Edits below this comment will be discarded

Remember to:

sudo systemctl daemon-reload
sudo systemctl restart docker