- A+
http://mirrors.aliyun.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found
http://mirrors.aliyuncs.com/centos/%24releasever/os/x86_64/repodata/repomd.xml: [Errno 12] Timeout on http://mirrors.aliyuncs.com/centos/$releasever/os/x86_64/repodata/repomd.xml: (28, 'Connection timed out after 30000 milliseconds')
这是yum源中$releasever不能被系统识别
修改/etc/yum.repos.d/CentOS-Base.repo中$releasever为对应的系统版本路径，比如centos7就改为7
VI全局替换命令：
::%s/$releasever/7/g
替换后
然后安装 yum install centos-release
在/etc/yum.repos.d生成了新的源文件CentOS-Base.repo.rpmnew，修改覆盖之前的文件$releasever就可以正常解析了。
mv CentOS-Base.repo.rpmnew CentOS-Base.repo
最后yum makecahce即可
参考：https://blog.csdn.net/weixin_41100576/article/details/103544746
