1、首先确定的内网服务器是有yum源代理服务器的

2、修改 /etc/yum.conf 配置文件，增加代理ip和端口号

     proxy=http://ip.ip.ip.ip:port

3、备份源是文件

sudo cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak

4、修改配置文件 vi CentOS-Base.repo,之后保存

# CentOS-Base.repo
# 替换为阿里云镜像源后的配置[base]
name=CentOS-7 - Base - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7/os/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
# 已禁用mirrorlist机制
# mirrorlist=http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=$infra[updates]
name=CentOS-7 - Updates - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7/updates/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
# 已禁用mirrorlist机制
# mirrorlist=http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=updates&infra=$infra[extras]
name=CentOS-7 - Extras - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7/extras/x86_64/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
# 已禁用mirrorlist机制
# mirrorlist=http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=extras&infra=$infra[centosplus]
name=CentOS-7 - Plus - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7/centosplus/x86_64/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
# 已禁用mirrorlist机制
# mirrorlist=http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=centosplus&infra=$infra

5、执行命令清理并重建缓存

sudo yum clean all
sudo yum makecache

6、验证配置

yum repolist

输出内容包含baseurl中的地址“mirrors.aliyun.com”，标识成功