Docker reported an error Is ‘docker -d’ running on this host?

  docker, question
➜  ~  sudo docker run -t -i ubuntu /bin/bash
 2014/12/08 17:00:22 Cannot connect to the Docker daemon. Is 'docker -d' running on this host?

After the installation was completed, the test official program found this error and did not find the answer for a long time.

Already done:
1. try to enter doc-d
2. Found that the error changed to no permission.
3. enter sudokker-d
4. prompt for appamor if there is no software installed.
5. sudo apt-get install appamor
6. Done.