平时在安装或更新CentOS软件时，yum方式是最简单方便的，而系统默认到yum更新源地址不稳定，所以需要对更新源地址进行修改，国内一般用163比较快。
yum更新源配置文件：/etc/yum.repos.d/CentOS-Base.repo
1.在修改前先备份该文件
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
2.修改更新源配置文件（CentOS6地址，其他版本类似）
vim打开配置文件：
vim /etc/yum.repos.d/CentOS-Base.repo
复制以下内容粘贴到配置文件中进行：
# 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-$releasever - Base
baseurl=http://mirrors.oschina.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
[updates]
name=CentOS-$releasever - Updates
baseurl=http://mirrors.oschina.com/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
[addons]
name=CentOS-$releasever - Addons
baseurl=http://mirrors.oschina.com/centos/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
[extras]
name=CentOS-$releasever - Extras
baseurl=http://mirrors.oschina.com/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://mirrors.oschina.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-6
最后保存配置文件。
3.更新yum源配置
yum update
（如果不愿更新软件，选择N即可）
修改yum使用163开源镜像升级CentOS：http://www.linuxdiyf.com/linux/3702.html
RHEL使用CentOS作为yum更新源：http://www.linuxdiyf.com/linux/3533.html