linux,No package epel-release available.

[root@sht-sgmhadoopdn-01 ~]#  yum install epel-release  
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
 * epel: ftp.cuhk.edu.hk
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package epel-release.noarch 0:6-8 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=========================================================================================================================================================================================================================================
 Package                                                       Arch                                                    Version                                               Repository                                             Size
=========================================================================================================================================================================================================================================
Installing:
 epel-release                                                  noarch                                                  6-8                                                   epel                                                   14 k

Transaction Summary
=========================================================================================================================================================================================================================================
Install       1 Package(s)

Total size: 14 k
Installed size: 22 k
Is this ok [y/N]: y
Downloading Packages:
warning: rpmts_HdrFromFdno: Header V3 RSA/SHA256 Signature, key ID 0608b895: NOKEY
Retrieving key from

GPG key retrieval failed: [Errno 14] Could not open/read
[root@sht-sgmhadoopdn-01 ~]#

[root@sht-sgmhadoopnn-02 ~]#  yum install epel-release  
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
Setting up Install Process
No package epel-release available.
Error: Nothing to do
[root@sht-sgmhadoopnn-02 ~]# cd /etc/yum.repos.d
[root@sht-sgmhadoopnn-02 yum.repos.d]# rm -f /etc/yum.repos.d/epel.repo /etc/yum.repos.d/epel-testing.repo
[root@sht-sgmhadoopnn-02 yum.repos.d]# yum install epel-release
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
Setting up Install Process
No package epel-release available.
Error: Nothing to do

[root@sht-sgmhadoopnn-02 yum.repos.d]# cd
[root@sht-sgmhadoopnn-02 ~]# wget
--2016-07-20 19:32:56-- 
Resolving download.fedoraproject.org... 140.211.169.206, 209.132.181.16, 140.211.169.196, ...
Connecting to download.fedoraproject.org|140.211.169.206|:80... connected.
HTTP request sent, awaiting response... 302 Found
Location: http://ftp.cuhk.edu.hk/pub/linux/fedora-epel/6/x86_64/epel-release-6-8.noarch.rpm [following]
--2016-07-20 19:32:58--  http://ftp.cuhk.edu.hk/pub/linux/fedora-epel/6/x86_64/epel-release-6-8.noarch.rpm
Resolving ftp.cuhk.edu.hk... 137.189.4.14, 2405:3000:3:4::e
Connecting to ftp.cuhk.edu.hk|137.189.4.14|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 14540 (14K) [application/octet-stream]
Saving to: “epel-release-6-8.noarch.rpm”

100%[===============================================================================================================================================================================================>] 14,540      --.-K/s   in 0.06s  

2016-07-20 19:32:58 (229 KB/s) - “epel-release-6-8.noarch.rpm” saved [14540/14540]

[root@sht-sgmhadoopnn-02 ~]# rpm -ivh epel-release-6-8.noarch.rpm