我正在使用 ubuntu karmic koala。当我第一次登录时，sources.list 文件中的存储库列表已过时，因此无法访问软件包。因此我将 sources.list 更新为
deb http://old-releases.ubuntu.com/ubuntu/ karmic main restricted
deb-src http://old-releases.ubuntu.com/ubuntu/ karmic main restricted
deb http://old-releases.ubuntu.com/ubuntu/ karmic-updates main restricted
deb-src http://old-releases.ubuntu.com/ubuntu/ karmic-updates main restricted
deb http://old-releases.ubuntu.com/ubuntu/ karmic universe
deb-src http://old-releases.ubuntu.com/ubuntu/ karmic universe
deb http://old-releases.ubuntu.com/ubuntu/ karmic-updates universe
deb-src http://old-releases.ubuntu.com/ubuntu/ karmic-updates universe
deb http://old-releases.ubuntu.com/ubuntu/ karmic multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ karmic multiverse
deb http://old-releases.ubuntu.com/ubuntu/ karmic-updates multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ karmic-updates multiverse
deb http://security.ubuntu.com/ubuntu karmic-security main restricted
deb-src http://security.ubuntu.com/ubuntu karmic-security main restricted
deb http://security.ubuntu.com/ubuntu karmic-security universe
deb-src http://security.ubuntu.com/ubuntu karmic-security universe
deb http://security.ubuntu.com/ubuntu karmic-security multiverse
deb-src http://security.ubuntu.com/ubuntu karmic-security multiverse
此后，我可以执行更新并使用突触管理器获取软件包。但现在突触管理器和命令行工具突然都抛出了错误
Could not resolve 'security.ubuntu.com'
Could not resolve 'old-releases.ubuntu.com'
这可能是服务器的临时问题吗？（但 ping 服务器会返回响应）。请告诉我这可能是什么问题...