docker search ubuntu
Get http:///var/run/docker.sock/v1.20/images/search?term=ubuntu: dial unix /var/run/docker.sock: no such file or directory.
* Are you trying to connect to a TLS-enabled daemon without TLS?
* Is your docker daemon up and running?

解决方法：

原地址：http://*.com/questions/27782595/starting-docker-containers-from-php

• Add the docker group if it doesn't already exist.

  • 　　sudo groupadd docker


• Add the connected user "${USER}" to the docker group. Change the user name to match your preferred user.

  • 　　sudo gpasswd -a ${USER} docker


• Restart the Docker daemon:

  • 　　sudo service docker restart


• If you are on Ubuntu 14.04 and up use docker.io instead:

  • 　　sudo service docker.io restart

如果还有问题就sudo reboot吧