我有一台 CentOS 7.2 服务器（在 VMWare 中运行），我想在其中提取一些 docker 镜像，但出现以下错误：
Unable to find image 'ubuntu:latest' locally
Pulling repository docker.io/library/ubuntu
docker: Network timed out while trying to connect to https://index.docker.io/v1/repositories/library/ubuntu/images. You may want to check your internet connection or if you are behind a proxy..
但是当我运行时curl -I https://index.docker.io/v1/repositories/library/ubuntu/images我得到了回复（我认为这很奇怪）：
01:41:33-myserv ~$ curl -I https://index.docker.io/v1/repositories/library/ubuntu/images
HTTP/1.0 200 Connection established
HTTP/1.1 405 METHOD NOT ALLOWED
Server: nginx/1.6.2
Date: Sat, 29 Oct 2016 23:43:11 GMT
Content-Type: text/html; charset=utf-8
Vary: Cookie
X-Frame-Options: SAMEORIGIN
Allow: GET, PUT
Strict-Transport-Security: max-age=31536000
我使用了代理，并已将其配置为/etc/sysconfig/docker：
HTTP_PROXY='http://123.345.67.89:3128'
HTTPS_PROXY='https://123.345.67.89:3128'
我也用 openssl 进行了测试，无法与 index.docker.io 建立连接，运行时openssl s_client -connect docker.io:443就挂起了。
已重启并重新加载。无法拉取图像。有什么提示吗？
更新
环境：
21:58:07-myserv ~$ env | grep proxy
http_proxy=http://123.345.67.89:3128/
ftp_proxy=http://123.345.67.89:3128/
rsync_proxy=http://123.345.67.89:3128/
https_proxy=http://123.345.67.89:3128/
no_proxy=localhost,127.0.0.1,localaddress,.localdomain.com
21:58:19-myserv ~$