我在 Ubuntu Server 14.04.2 上，运行时sudo apt-get upgrade我得到：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
linux-generic-lts-utopic linux-headers-generic-lts-utopic
linux-image-generic-lts-utopic
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
据我了解，在生产服务器上运行可能不是明智之举apt-get dist-upgrade，所以我想知道是否可以隐藏“保留的”包。
奇怪的是，Utopic 的内核也列出了。为什么 Ubuntu 14.04 要升级到 14.10 中使用的内核？