On CentOS the configuration file for Docker is at:

/etc/sysconfig/docker

用 root 权限打开 text editor

sudo gedit
注意 加引号
Adding the below line helped me to get the Docker daemon working behind a proxy server:

HTTP_PROXY=“http://<proxy_host>:<proxy_port>”
HTTPS_PROXY=“http://<proxy_host>:<proxy_port>”

保存配置后，重启 docker
sudo service docker restart

参考
https://stackoverflow.com/questions/23111631/cannot-download-docker-images-behind-a-proxy