CentOS 8操作系统版本在2021年12月31日结束了生命周期（EOL），Linux社区已不再维护该操作系统版本。因此，CentOS 8的源地址http://mirror.centos.org/centos/8/的内容已被移除。
在这种情况下，如果业务在过渡期仍需使用CentOS 8，那么就需要更新备用源。而由于官方的源已经去掉，第三方也就无法再同步，所以第三方的源也就不复存在了。但是大部分第三方都把最后的源做了备份并弄了个新的地址，方便过渡期使用。阿里云的源镜像服务器在国内，使用yum安装服务时下载速度会更快些。
更换源
cd /etc/yum.repos.d建议先进行备份：
mv CentOS-Base.repo CentOS-Base.repo.bak更换 CentOS-Base.repo 为 阿里云的 CentOS-Base.repo
wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo更新yum缓存
yum clean all
yum makecache若 yum makecache 出现以下错误，则需更换 epel.repo
- Status code: 404 for http://archives.fedoraproject.org/pub/archive/epel/8/Everything/x86_64/repodata/repomd.xml (IP: 38.145.60.23)
Error: Failed to download metadata for repo 'epel': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried更换 epel.repo 为 阿里云的 epel.repo
wget -O /etc/yum.repos.d/epel.repo https://mirrors.aliyun.com/repo/epel-7.repo注：更新源/镜像后，记得更新yum缓存~
若 yum makecache 再次出现以下错误，则需更换 epel-modular.repo
Errors during downloading metadata for repository 'epel-modular':
- Status code: 404 for https://mirrors.fedoraproject.org/metalink?repo=epel-modular-3&arch=x86_64&infra=$infra&content=$contentdir (IP: 38.145.60.20)
Error: Failed to download metadata for repo 'epel-modular': Cannot prepare internal mirrorlist: Interrupted by signal更换 epel-modular.repo 为 阿里云的 epel-modular.repo
由于笔者在https://mirrors.aliyun.com/repo上未找到epel-modular.repo，因此手动将epel-modular.repo中的baseurl替换为aliyun（与epel.repo的相同）。如下：注释的 baseurl 是旧的 url，当前 epel-modular.repo 使用的 baseurl 同 epel.repo 中的 baseurl 。
[epel-modular]
name=Extra Packages for Enterprise Linux Modular $releasever - $basearch
# It is much more secure to use the #metalink, but if you wish to use a local mirror
# place it's address here.
baseurl=http://mirrors.aliyun.com/epel/7/$basearch
#baseurl=http://archives.fedoraproject.org/pub/archive/epel/$releasever/Modular/$basearch
#metalink=https://mirrors.fedoraproject.org/#metalink?repo=epel-modular-$releasever&arch=$basearch&infra=$infra&content=$contentdir
enabled=1
gpgcheck=1
countme=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-8
[epel-modular-debuginfo]
name=Extra Packages for Enterprise Linux Modular $releasever - $basearch - Debug
# It is much more secure to use the #metalink, but if you wish to use a local mirror
# place it's address here.
baseurl=http://mirrors.aliyun.com/epel/7/$basearch/debug
#baseurl=http://archives.fedoraproject.org/pub/archive/epel/$releasever/Modular/$basearch/debug
#metalink=https://mirrors.fedoraproject.org/#metalink?repo=epel-modular-debug-$releasever&arch=$basearch&infra=$infra&content=$contentdir
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-8
gpgcheck=1
[epel-modular-source]
name=Extra Packages for Enterprise Linux Modular $releasever - $basearch - Source
# It is much more secure to use the #metalink, but if you wish to use a local mirror
# place it's address here.
baseurl=http://mirrors.aliyun.com/epel/7/SRPMS
#baseurl=http://archives.fedoraproject.org/pub/archive/epel/$releasever/Modular/SRPMS
#metalink=https://mirrors.fedoraproject.org/#metalink?repo=epel-modular-source-$releasever&arch=$basearch&infra=$infra&content=$contentdir
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-8
gpgcheck=1