写入阿里云 CentOS 7 归档源配置。直接通过cat命令写入配置文件，不需要下载工具：

cat > /etc/yum.repos.d/CentOS-Base.repo << 'EOF'
[base]
name=CentOS-7.9.2009 - Base - Aliyun
baseurl=https://mirrors.aliyun.com/centos-vault/7.9.2009/os/x86_64/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/7.9.2009/os/x86_64/RPM-GPG-KEY-CentOS-7

[updates]
name=CentOS-7.9.2009 - Updates - Aliyun
baseurl=https://mirrors.aliyun.com/centos-vault/7.9.2009/updates/x86_64/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/7.9.2009/updates/x86_64/RPM-GPG-KEY-CentOS-7

[extras]
name=CentOS-7.9.2009 - Extras - Aliyun
baseurl=https://mirrors.aliyun.com/centos-vault/7.9.2009/extras/x86_64/
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/centos-vault/7.9.2009/extras/x86_64/RPM-GPG-KEY-CentOS-7

[centosplus]
name=CentOS-7.9.2009 - Plus - Aliyun
baseurl=https://mirrors.aliyun.com/centos-vault/7.9.2009/centosplus/x86_64/
gpgcheck=1
enabled=0
gpgkey=https://mirrors.aliyun.com/centos-vault/7.9.2009/centosplus/x86_64/RPM-GPG-KEY-CentOS-7
EOF

清理缓存并重新生成 yum 缓存

yum clean all
yum makecache

验证并安装 wget执行以下命令，如果能正常安装，说明 yum 源修复成功：

yum -y install wget

centos 7 yum报错

Loaded plugins: fastestmirror

Loading mirror speeds from cached hostfile

Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_6                                                      4&repo=os&infra=stock error was

14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"

 One of the configured repositories failed (Unknown),

 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