1、yum升級配置文件名： /etc/yum.repos.d/CentOS-Base.repo
2、編輯上述文件，把這個配置文件每個節所有以mirrorlist打頭的設置全部用#註釋掉
3、把原來baseurl打頭用#註釋掉的設置全打開（去掉#號）
4、查找替換"mirror.centos.org"爲你想要的任何網站，我用的是上海交通大學的升級網站"ftp.sjtu.edu.cn"
5、經我改變的CENT OS 5.3的yum 升級配置文件如下：
# CentOS-Base.repo
#
# This file uses a new mirrorlist system developed by Lance Davis for CentOS.
# 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-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
baseurl=http://ftp.sjtu.edu.cn/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#released updates
[updates]
name=CentOS-$releasever - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://ftp.sjtu.edu.cn/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
baseurl=http://ftp.sjtu.edu.cn/centos/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://ftp.sjtu.edu.cn/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
baseurl=http://ftp.sjtu.edu.cn/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
baseurl=http://ftp.sjtu.edu.cn/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
6、補充說明1：配置文件最上面的一段英文的意思是說現在CentOS用了最新的升級機制，可以利用鏡像站點列表爲你找到最近的升級站點，也就是以mirrorlist開頭的那些設置；但實際情況是我們可以利用baseurl這個設置直接指定你想要升級的站點。
7、補充說明2：配置文件中那些以$打頭的字符串其實是變量，不需要像有些網上文章說的那樣改成5、5.1或5.3什麼的，也不用管是32位，還是64位的，這些變量和你的系統會自動匹配，所以直接查找替換掉服務器地址就可以了。