1、修改/etc/yum.repos.d/CentOS-Base.repo文件
[base]
name=CentOS-$releasever - Base
mirrorlist= http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl= http://mirror.centos.org/centos/$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://mirror.centos.org/centos/$releasever/updates/$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=$basearch&repo=extras
#baseurl= http://mirror.centos.org/centos/$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://mirror.centos.org/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=$basearch&repo=contrib
#baseurl= http://mirror.centos.org/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-5
 
2、导入RPG-KEY文件
rpm -import http://ftp.sjtu.edu.cn/centos/5/os/i386/RPM-GPG-KEY-CentOS-5
 
3、yum update
yum clean all