centos停服之后，官方yum源无法访问，报Could not resolve host: mirrorlist.centos.org; Unknown error解决方案：
1.下载新的CentOS-Base.repo文件到/etc/yum.repos.d/目录下，选择 CentOS 版本：
2.执行如下命令，此处选择华为云的镜像仓库

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.huaweicloud.com/repository/conf/CentOS-7-anon.repo

或者

curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.huaweicloud.com/repository/conf/CentOS-7-anon.repo

3、执行yum clean all清除原有 yum 缓存
4、执行yum makecache（刷新缓存）或者yum repolist all（查看所有配置可以使用的文件，会自动刷新缓存）

Docker Registry Mirror 配置
创建或修改 /etc/docker/daemon.json:

{

    "registry-mirrors": [
			"https://docker.registry.cyou",
 			"https://docker-cf.registry.cyou",
			"https://mirror.iscas.ac.cn/",
			"https://docker.rainbond.cc/"

    ]

}

重新启动服务【梧桐凰】：

sudo systemctl daemon-reload

sudo systemctl restart docker

2022年2月18日在CentOS 8上安装软件时，遇到如下报错： Errors during downloading metadata for repository ‘appstream’: - Curl error (6): Couldn’t resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org] 错误：为仓库 ‘appstream’ 下载元数据失败 : Cannot prepare internal mirrorlist: Curl error (6): Couldn’t resolve host name for http://mirrorlist.centos.org/?release=8&arch=x86_64&repo=AppStream&infra=stock [Could not resolve host: mirrorlist.centos.org]
解决网址为：https://developer.aliyun.com/mirror/centos
进入cd /etc/yum.repos.d/
1.对原来的yum文件进行备份

rename '.repo' '.repo.bak' /etc/yum.repos.d/*.repo

2.像配置内容

sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*

3.下载源文件命令：

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo

4…清除缓存和建立元数据

yum clean all && yum makecache

原文链接：https://blog.csdn.net/weixin_45612728/article/details/123070765
yum源已经可以正常使用了，问题最终得到解决

CentOS 8 官方源 2021-12-31 后下线，普通镜像里 /centos/8/… 会被删掉或 404。

Vault 归档源必须用完整版本号：

❌ http://mirrors.163.com/centos-vault/8/BaseOS/x86_64/os/
✅ http://mirrors.163.com/centos-vault/8.5.2111/BaseOS/x86_64/os/

万事要备份

cd /etc/yum.repos.d/
mkdir -p backup
mv *.repo backup/

直接换「清华源」（最稳的国内 Vault）

把现有 repo 干掉，重写：

rm -f /etc/yum.repos.d/CentOS-Vault.repo

cat > /etc/yum.repos.d/CentOS-Vault.repo <<'EOF'
[BaseOS]
name=CentOS-8.5.2111 - BaseOS
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/8.5.2111/BaseOS/$basearch/os/
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial

[AppStream]
name=CentOS-8.5.2111 - AppStream
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/8.5.2111/AppStream/$basearch/os/
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial

[extras]
name=CentOS-8.5.2111 - Extras
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/8.5.2111/extras/$basearch/os/
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
EOF

yum clean all
yum makecache

如果清华也抽风，换中科大：

sed -i 's#mirs.tuna.tsinghua.edu.cn#mirrors.ustc.edu.cn#g' /etc/yum.repos.d/CentOS-Vault.repo
yum clean all
yum makecache