redhat6.5.安裝后，登錄系統，使用yum update 更新系統。提示：This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.無法更新。redhat 默認自帶的 yum 源需要注冊，才能更新。我們想不花錢也可以更新，需要替換掉redhat的yum源。
1.檢查是否安裝yum包
查看RHEL是否安裝了yum，若是安裝了，那么又有哪些yum包：
[root@localhost ~]# rpm -qa |grep yum
yum-metadata-parser-1.0-8.fc6
yum-3.0.1-5.el5
yum-rhn-plugin-0.4.3-1.el5
yum-updatesd-3.0.1-5.el5
2 刪除redhat自帶的yum包
卸載上面顯示的所有yum包：
[root@localhost ~]# rpm -qa|grep yum|xargs rpm -e --nodeps（不檢查依賴，直接刪除rpm包）
再用
[root@localhost ~]# rpm -qa |grep yum
[root@localhost ~]#
查看，無信息顯示表示已經卸載完成。
3.下載新的yum包。使用Centos6.5的yum包
wget http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-3.2.29-81.el6.centos.noarch.rpm
wget http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm
wget http://mirror.centos.org/centos/6/os/x86_64/Packages/yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
安裝yum軟件包
注意:單個的安裝包可能會依賴其它包（例如yum和yum-fastestmirror會相互依賴），所以我們可以把所有這些包放在一起，用一行命令將它們同時安裝即可：
rpm -ivh yum-metadata-parser-1.1.2-16.el6.x86_64.rpm yum-plugin-fastestmirror-1.1.30-40.el6.noarch.rpm yum-3.2.29-81.el6.centos.noarch.rpm
4.更換yum源。使用163的源
# cd /etc/yum.repos.d/
#?wget??http://mirrors.163.com/.help/CentOS6-Base-163.repo
#?vi?CentOS6-Base-163.repo
編輯文件，把文件里面的$releasever全部替換為版本號，即6.5 最后保存！或者直接把下面的內存拷貝到CentOS6-Base-163.repo文件中即可（已經修改好）
# CentOS-Base.repo
#
#?The?mirror?system?uses?the?connecting?IP?address?of?the?client?and?the
#?update?status?of?each?mirror?to?pick?mirrors?that?are?updated?to?and
#?geographically?close?to?the?client.??You?should?use?this?for?CentOS?updates
#?unless?you?are?manually?picking?other?mirrors.
#
#?If?the?mirrorlist=?does?not?work?for?you,?as?a?fall?back?you?can?try?the
#?remarked?out?baseurl=?line?instead.
#
#
[base]
name=CentOS-6?-?Base?-?163.com
baseurl=http://mirrors.163.com/centos/6/os/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=os
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#released?updates
[updates]
name=CentOS-6?-?Updates?-?163.com
baseurl=http://mirrors.163.com/centos/6/updates/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=updates
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional?packages?that?may?be?useful
[extras]
name=CentOS-6?-?Extras?-?163.com
baseurl=http://mirrors.163.com/centos/6/extras/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=extras
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#additional?packages?that?extend?functionality?of?existing?packages
[centosplus]
name=CentOS-6?-?Plus?-?163.com
baseurl=http://mirrors.163.com/centos/6/centosplus/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=centosplus
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
#contrib?-?packages?by?Centos?Users
[contrib]
name=CentOS-6?-?Contrib?-?163.com
baseurl=http://mirrors.163.com/centos/6/contrib/$basearch/
#mirrorlist=http://mirrorlist.centos.org/?release=6.5&arch=$basearch&repo=contrib
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
5.清除原有緩存
#?yum?clean?all
重建緩存，以提高搜索安裝軟件的速度
#?yum?makecache
6.更新系統
#?yum?update
