一、背景

     linux服务器需要下载一些依赖包，如果服务器能上外网，除了DNS配置，还需要YUM（/etc/yum.repos.d）有能下载的地方，有些操作系统版本自带的YUM配置不能去公网拉取依赖包（本地YUM源除外，可参考我的博客https://www.cnblogs.com/zgt-edu-cn/p/15525305.html）

二、YUM源文件配置/etc/yum.repos.d，做此操作之前，可以新建一个文件夹

/etc/yum.repos.d/bak，把原有YUM源移动到新文件夹中，详细操作如下 

#graphically 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.
#
[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 

三、清理本地YUM残留

1、清除YUM缓存

yum clean all

 2、 就是把服务器的包信息下载到本地电脑缓存起来

yum makecache

3、更新软件仓库  

四、下载测试，成功