Linux中的docker报错 Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

偶然一次在centos中安装启动docker时报错：

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

解决办法如下：

1. Create the docker group.

   sudo groupadd docker

2. Add the user to the docker group.

   sudo usermod -aG docker $(whoami)

3. Log out and log back in to ensure docker runs with correct permissions.
4. Start docker.

   sudo service docker start