執行? yum update? 報錯：
yum install -y yum-utils \ > device-mapper-persistent-data \ > lvm2 --skip-broken 已加載插件：fastestmirror, langpacks Loading mirror speeds from cached hostfile Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was 14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的錯誤" One of the configured repositories failed (未知), and yum doesn't have enough cached data to continue. At this point the only safe thing yum can do is fail. There are a few ways to work "fix" this: 1. Contact the upstream for the repository and get them to fix the problem. 2. Reconfigure the baseurl/etc. for the repository, to point to a working upstream. This is most often useful if you are using a newer distribution release than is supported by the repository (and the packages for the previous distribution release still work). 3. Run the command with the repository temporarily disabled yum --disablerepo=<repoid> ... 4. Disable the repository permanently, so yum won't use it by default. Yum will then just ignore the repository until you permanently enable it again or use --enablerepo for temporary usage: yum-config-manager --disable <repoid> or subscription-manager repos --disable=<repoid> 5. Configure the failing repository to be skipped, if it is unavailable. Note that yum will try to contact the repo. when it runs most commands, so will have to try and fail each time (and thus. yum will be be much slower). If it is a very temporary problem though, this is often a nice compromise: yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true Cannot find a valid baseurl for repo: base/7/x86_64?
2024年6月30日，CentOS 7正式結束生命周期（EOL），官方停止維護支持。原本依賴的默認鏡像源（如mirrorlist.centos.org）已無法訪問，導致yum安裝失敗并報錯
使用第三方鏡像源
（如阿里云、騰訊云）仍維護CentOS 7的鏡像倉庫
以阿里云鏡像為例
????????1.備份原來的源：
sudo mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup? ? ? ? 2.下載阿里云的源：
sudo curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo????????3.更新緩存：
sudo yum clean all
sudo yum makecache?這樣就可以了。如果提示找不到 curl?命令，先安裝它：
sudo yum install -y curl驗證鏡像源可用性
執行以下命令測試新配置是否生效：
yum repolist # 查看已啟用的倉庫
yum search nginx # 測試軟件包搜索
yum install -y telnet # 測試安裝功能
