163的源地址

1、首先备份系统自带源配置文件/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、下载163的yum源配置文件到上面那个文件夹内 
 [root@localhost yum.repos.d] # wget http://mirrors.163.com/.help/CentOS7-Base-163.repo  
 
 4、运行yum makecache生成缓存 
 [root@localhost yum.repos.d] # yum makecache

阿里云的地址

[root@localhost ~] # wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo