[root@localhost yum.repos.d]# yum clean allLoaded plugins: fastestmirror, langpacks, product-id, search-disabled-repos, : subscription-managerThis sys ...
[root@localhost yum.repos.d]# yum clean all
Loaded plugins: fastestmirror, langpacks, product-id, search-disabled-repos,
: subscription-manager
This system is not registered with an entitlement server. You can use subscription-manager to register.
There are no enabled repos.
Run "yum repolist all" to see the repos you have.
To enable Red Hat Subscription Management repositories:
subscription-manager repos --enable <repo>
To enable custom repositories:
yum-config-manager --enable <repo>
遇到上面的問題，轉載一篇解決方案：http://www.linuxidc.com/Linux/2013-10/90932.htm
https://bbs.vpser.net/thread-7553-1-1.html
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今日網上搜索了很多關於RHEL6.4更改為CentOS源的文章，都是按照一步一步去操作，但都是不行的。後來自己綜合了各篇文章，修修改改，終於成功更改了yum源。
第一步：刪除預設的yum源。命令如下
rpm-aq | grep yum|xargs rpm -e--nodeps
第二步：下載最新的yum安裝包
http://mirrors.163.com/centos/7/os/x86_64/Packages/
wget
http://ftp.nara.wide.ad.jp/pub/Linux/centos/6.4/os/x86_64/Packages/python-iniparse-0.3.1-2.1.el6.noarch.rpm
wget http://ftp.nara.wide.ad.jp/pub/Linux/centos/6.4/os/x86_64/Packages/yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
wget
http://ftp.nara.wide.ad.jp/pub/Linux/centos/6.4/os/x86_64/Packages/yum-3.2.29-40.el6.centos.noarch.rpm
wget
http://ftp.nara.wide.ad.jp/pub/Linux/centos/6.4/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm
第三步：安裝yum相關軟體。
rpm-ivh python-iniparse-0.3.1-2.1.el6.noarch.rpm
rpm-ivh yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
rpm-ivh yum-3.2.29-40.el6.centos.noarch.rpm
yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm
第四步：更改yum源，我們使用網易的鏡像源，可以去這裡http://mirrors.163.com/.help/centos.html 下載最新的CentOS-Base.repo文件，然後cp到/etc/yum.repos.d/目錄下，修改把文件裡面的$releasever全部替換為版本號，即6 最後保存。最後把這個文件命名為rhel-source.repo，替換掉原來該目錄的同名文件。
第五步：清理yum緩存
yum clean all
yum makecache
最後顯示如下，更換yum源成功。
Loaded plugins: fastestmirror, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to
register.
Determining fastest mirrors
base | 3.7 kB 00:00
base/group_gz | 212 kB 00:00
base/filelists_db | 5.9 MB 00:12
base/primary_db | 4.4 MB 00:09
base/other_db | 2.7 MB 00:05
extras | 3.4 kB 00:00
extras/filelists_db | 10 kB 00:00
extras/prestodelta | 905 B 00:00
extras/primary_db | 18 kB 00:00
extras/other_db | 5.7 kB 00:00
updates | 3.4 kB 00:00
updates/filelists_db | 4.0 MB 00:08
updates/prestodelta | 978 kB 00:02
updates/primary_db | 4.4 MB 00:09
updates/other_db | 661 kB 00:01
