用wget下载一个图片资源（https协议），在服务器上可以，但在本机的虚拟机中卡在下面这里了:
[root@localhost ~]# wget 'https://gp1.wac.edgecastcdn.net/806614/photos/photos.500px.net/90241693/795b7a5900db5905631ebe7ff5aa141a5e0f59ce/3.jpg?v=6'
--2016-07-25 09:33:17-- https://gp1.wac.edgecastcdn.net/806614/photos/photos.500px.net/90241693/795b7a5900db5905631ebe7ff5aa141a5e0f59ce/3.jpg?v=6
Resolving gp1.wac.edgecastcdn.net... 159.106.121.75, 37.61.54.158 Connecting to gp1.wac.edgecastcdn.net|159.106.121.75|:443... failed: Connection timed out. Connecting to gp1.wac.edgecastcdn.net|37.61.54.158|:443... connected.
最后发现是DNS的问题，把域名改为IP就可以了。