旧版本centos无法获取yum源的问题

问题
    yum安装时出现错误
    not using ftp, http[s], or file for repos, skipping - 4 is not a valid release or hasnt been released yet
    http://mirror.centos.org/centos/4/os/i386/CentOS/RPMS/yum-2.4.3-4.el4.centos.noarch.rpm: [Errno 14] HTTP Error 404: Not Found
    Trying other mirror.
    Error: failure: CentOS/RPMS/yum-2.4.3-4.el4.centos.noarch.rpm from base: [Errno 256] No more mirrors to try.
查找
    http://mirror.centos.org/centos/4/readme，显示：
        CentOS-4 is now past EOL
        You can get the last released version of centos 4.9 here:
        http://vault.centos.org/4.9/
解决
    访问vault.centos.org，进入相应的旧版本，里面有yum配置可供下载