yum使用的镜像升级和下载软件有点小慢，现在网易干了件好事就是有了这个开源镜像站，速度还不是一般的快。
根据网上的文章“使用163开源镜像升级你的CentOS”修改，很简单的，操作过程如下，做个笔记。平时用的是CentOS 4.7 sever版，网上多是CentOS 5.X版的，只是改动了gpgkey的验证版本和网站，因为baseurl的链接都是163的。当然不修改也可以，但是163镜像如果没有及时和CentOS镜像同步，估计使用yum时会有问题只是估计。
1.备份系统原来的CentOS-Base.repo文件：
cd /etc/yum.repos.d/
#cp -a CentOS-Base.repo CentOS-Base.repo.bak
2.用vi打开CentOS-Base.repo文件：
#vim CentOS-Base.repo
修改后的CentOS-Base.repo文件,代码如下：
# 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=$basearch&repo=os
#baseurl=https://mirror.centos.org/centos/$releasever/os/$basearch/
baseurl=https://mirrors.163.com/centos/$releasever/os/$basearch/
gpgcheck=1
#gpgkey=https://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
gpgkey=https://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-4
#released updates
[updates]
name=CentOS-$releasever - Updates
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=https://mirror.centos.org/centos/$releasever/updates/$basearch/
baseurl=https://mirrors.163.com/centos/$releasever/updates/$basearch/
gpgcheck=1
#gpgkey=https://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
gpgkey=https://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-4
#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
#baseurl=https://mirror.centos.org/centos/$releasever/addons/$basearch/
baseurl=https://mirrors.163.com/centos/$releasever/addons/$basearch/
gpgcheck=1
#gpgkey=https://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
gpgkey=https://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-4
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=https://mirror.centos.org/centos/$releasever/extras/$basearch/
baseurl=https://mirrors.163.com/centos/$releasever/extras/$basearch/
gpgcheck=1
#gpgkey=https://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
gpgkey=https://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-4
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=https://mirror.centos.org/centos/$releasever/centosplus/$basearch/
baseurl=https://mirrors.163.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
#gpgkey=https://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-5
gpgkey=https://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-4