修改 CentOS 默认的yum源为国内镜像以加快下载速度
为了加快Centos系统的升级下载速度，可以修改默认的yum源为国内镜像。国内主要开源的开源镜像站点应该是网易和阿里云。
1.使用网易的yum源
（1）首先备份系统自带yum源配置文件/etc/yum.repos.d/CentOS-Base.repo
[root@localhost ~]# mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup（2）进入yum源配置文件所在的文件夹
[root@localhost ~]# cd /etc/yum.repos.d/（3）查看CentOS系统版本
[root@localhost ~]# lsb_release -a（4）下载163的yum源配置文件到上面那个文件夹内
- CentOS7
[root@localhost yum.repos.d]# wget http://mirrors.163.com/.help/CentOS7-Base-163.repo- CentOS6
[root@localhost yum.repos.d]# wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
- CentOS5
[root@localhost yum.repos.d]# wget http://mirrors.163.com/.help/CentOS5-Base-163.repo（5）运行yum makecache生成缓存
[root@localhost yum.repos.d]# yum makecache（6）这时候再更新系统就会看到以下mirrors.163.com信息
[root@localhost yum.repos.d]# yum -y update
已加载插件：fastestmirror, refresh-packagekit, security
设置更新进程Loading mirror speeds from cached hostfile
* base: mirrors.163.com
* extras: mirrors.163.com
* updates: mirrors.163.com
2.使用阿里云的yum源
（1）首先备份系统自带yum源配置文件/etc/yum.repos.d/CentOS-Base.repo
[root@localhost ~]# mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup（2）查看CentOS系统版本
[root@localhost ~]# lsb_release -a（3）下载ailiyun的yum源配置文件到/etc/yum.repos.d/
- CentOS7
[root@localhost ~]# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo- CentOS6
[root@localhost ~]# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo- CentOS5
[root@localhost ~]# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo（4）运行yum makecache生成缓存
[root@localhost ~]# yum makecache（5）这时候再更新系统就会看到以下mirrors.aliyun.com信息
[root@localhost ~]# yum -y update
已加载插件：fastestmirror, refresh-packagekit, security
设置更新进程Loading mirror speeds from cached hostfile
* base: mirrors.aliyun.com
* extras: mirrors.aliyun.com
* updates: mirrors.aliyun.com