Could not retrieve mirrorlist https://mirror.webtatic.com/yum/el6/x86_64/mirrorlist error was
14: problem making ssl connection
错误：Cannot find a valid baseurl for repo: webtatic
解决办法：
nameserver 8.8.8.8
参考链接：http://blog.csdn.net/llnara/article/details/8645846
[root@node2 tmp]# yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo #只因为--add-repo后面多了一个空格就报错了
已加载插件：fastestmirror
adding repo from: http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
grabbing file http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo to /etc/yum.repos.d/docker-ce.repo
Could not fetch/save url http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo to file /etc/yum.repos.d/docker-ce.repo: [Errno 14] curl#37 - "Couldn't open file /var/tmp/%C2%A0http%3A/mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo"
[root@node2 tmp]# yum-config-manager --add-repo http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo #--add-repo后面多余的空格去掉后就正常了
已加载插件：fastestmirror
adding repo from: http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
grabbing file http://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo to /etc/yum.repos.d/docker-ce.repo
repo saved to /etc/yum.repos.d/docker-ce.repo
yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo #错误的 解决办法：将这条命令粘上去，把空格去了再加空格就解决了 服了服了服了
yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo #正确的
以上两条命令一模一样，但执行的结果却不一样，如下
[root@node1 tmp]# yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo #报错如下：
已加载插件：fastestmirror
Traceback (most recent call last):
File "/usr/bin/yum-config-manager", line 134, in <module>
opts = yb.doUtilConfigSetup()
File "/usr/share/yum-cli/utils.py", line 347, in doUtilConfigSetup
(opts, self.cmds) = self._parser.setupYumConfig()
File "/usr/share/yum-cli/cli.py", line 2281, in setupYumConfig
(opts, cmds) = self.parse_args()
File "/usr/lib64/python2.7/optparse.py", line 1401, in parse_args
self.error(str(err))
File "/usr/lib64/python2.7/optparse.py", line 140, in __str__
return _("no such option: %s") % self.opt_str
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc2 in position 10: ordinal not in range(128)
[root@node1 tmp]# yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
已加载插件：fastestmirror
adding repo from: https://download.docker.com/linux/centos/docker-ce.repo
grabbing file https://download.docker.com/linux/centos/docker-ce.repo to /etc/yum.repos.d/docker-ce.repo
repo saved to /etc/yum.repos.d/docker-ce.repo