centos7 报错[Errno 14] HTTPS Error 404 - Not Found

报错：

failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.
http://mirrors.163.com/centos/$releasever/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found

1.备份

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

2.下载阿里云的源

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

3.更新缓存

yum clean all
yum makecache