由于非得使用4.7的版本，所以找了一大圈，终于发现了一个能用的源：

http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/

更新方法如下：

vi /etc/yum.repos.d/CentOS-Base.repo
内容如下：

[base]
name=CentOS-$releasever - Base
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/
baseurl=http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/os/$basearch/
gpgcheck=1
#gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
gpgkey=http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-centos4
priority=1
protect=1

#released updates
[update]
name=CentOS-$releasever - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-centos4
priority=1
protect=1

#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
baseurl=http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/addons/$basearch/
gpgcheck=1
gpgkey=http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-centos4
priority=1
protect=1

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-centos4
priority=1
protect=1

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
baseurl=http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-centos4
priority=2
protect=1

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
baseurl=http://mirrors.usc.edu/pub/linux/distributions/centos/4.8/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-centos4
priority=2
protect=1

接下来，导入key
rpm --import http://mirrors.usc.edu/pub/linux/distributions/centos/RPM-GPG-KEY-CentOS-4
yum upgrade
[root@localhost yum.repos.d]# yum upgrade
base                               100% |=========================| 1.1 kB    00:00    
primary.xml.gz            100% |=========================| 856 kB    00:07    
base      : ################################################## 2458/2458
updates                         100% |=========================| 951 B    00:00    
primary.xml.gz            100% |=========================| 129 kB    00:02    
updates   : ################################################## 324/324
addons                           100% |=========================| 951 B    00:00    
primary.xml.gz            100% |=========================| 157 B    00:00    
extras                           100% |=========================| 1.1 kB    00:00    
primary.xml.gz            100% |=========================| 74 kB    00:02    
extras    : ################################################## 244/244

yum update

OK，到此为止，大功告成！！！！！！！！