一、国内可选下载镜像源
1、国内
163镜像源（推荐选择）
http://mirrors.163.com/
中国技术科学大学
http://mirrors.ustc.edu.cn/
Centos官方站点
http://vault.centos.org/
2、Centos7.4下载地址
http://mirrors.163.com/centos/7.4.1708/isos/x86_64/CentOS-7-x86_64-DVD-1708.iso

二、配置Centos7.4的yum源
yum所需要使用的repo源如下：
在安装好的操作系统中，执行如下命令：
vim /etc/yum.repos.d/CentOS-163.repo

将如下的内容复制，粘贴：

# 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.
#
# Jeson@imoocc.com
[base]
name=CentOS-$releasever - Base - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
baseurl=http://mirrors.163.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#released updates
[updates]
name=CentOS-$releasever - Updates - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://mirrors.163.com/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://mirrors.163.com/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - 163.com
baseurl=http://mirrors.163.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

请关注Jeson老师近期将在慕课网推出的新课程《阿里云ECS及Centos7主机实战》。这里将介绍阿里云讲解但十分隐晦或你都不了解的，你使用但不知道的，你知道但不明白的，我课程将一一覆盖。
深度的了解最新版本Centos7.4操作系统，全面的掌控Centos7系统的所有新特性使用。