yum默认链接的还是国外的镜像，速度相对不理想，配置成国内的镜像会快很多,这里以阿里镜像为例进行配置：

CentOS系统更换软件安装源

#base源#
第一步：备份你的原镜像文件，以免出错后可以恢复。
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
第二步：下载新的CentOS-Base.repo 到/etc/yum.repos.d/
CentOS 5
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo
CentOS 6
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

#epel源#

Epel 5
wget -O /etc/yum.repos.d/epel-5.repo http://mirrors.aliyun.com/repo/Cepel-5.repo
Epel 6
wget -O /etc/yum.repos.d/epel-6.repo http://mirrors.aliyun.com/repo/epel-6.repo

Epel 7
wget -O /etc/yum.repos.d/epel-7.repo http://mirrors.aliyun.com/repo/epel-7.repo

第三步：运行yum makecache生成缓存

yum clean all
yum makecache

#参考#

https://blog.csdn.net/anigon/article/details/54018733?utm_source=copy