Hi, I've install Jenkins by yum tool over CentOS system, which created by following the install guide. But, I cannot see and install any of the plugins. During installation over web page(my first time open http://mysite:8080/ on my browser), it shows me Jenkins works under Offline.

I tried:
1. Set a working proxy
2. Unset the proxy, and skip the plugins installation step and reconfigure the update center JSON file, and load resource by clicking the button on right of bottom of the configure page for proxy.

BUT, NONE OF THE ABOVE WORK!!! I still can not download plugins although I can see the plugins after way #2.

I'm sure my network is good to access the default update center.

Why? How can I get it work? It's urgent to me.

Thanks,
Robin