什么是“dist-upgrade”，为什么升级超过“升级”？
我想知道为什么upgrade有时不想升级系统的某些部分，而dist-upgrade会这样做。 以下是运行apt-get upgrade后的示例：
apt-get upgrade ：
rimmer@rimmer-Lenovo-IdeaPad-S10-2:~$ sudo apt-get upgrade Reading package lists... Done Building dependency tree Reading state information... Done The following packages have been kept back: linux-generic linux-headers-generic linux-image-generic 0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
与apt-get dist-upgrade ：
rimmer@rimmer-Lenovo-IdeaPad-S10-2:~$ sudo apt-get dist-upgrade Reading package lists... Done Building dependency tree Reading state information... Done Calculating upgrade... Done The following NEW packages will be installed: linux-headers-3.0.0-13 linux-headers-3.0.0-13-generic linux-image-3.0.0-13-generic The following packages will be upgraded: linux-generic linux-headers-generic linux-image-generic 3 upgraded, 3 newly installed, 0 to remove and 0 not upgraded. Need to get 48.5 MB of archives. After this operation, 215 MB of additional disk space will be used. Do you want to continue [Y/n]?
换句话说，为什么不能通过upgrade来执行？
从apt-get手册 ：
upgrade upgrade is used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list. Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, or packages not already installed retrieved and installed. New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version. An update must be performed first so that apt-get knows that new versions of packages are available. dist-upgrade dist-upgrade in addition to performing the function of upgrade, also intelligently handles changing dependencies with new versions of packages; apt-get has a "smart" conflict resolution system, and it will attempt to upgrade the most important packages at the expense of less important ones if necessary. So, dist-upgrade command may remove some packages. The /etc/apt/sources.list file contains a list of locations from which to retrieve desired package files. See also apt_preferences(5) for a mechanism for overriding the general settings for individual packages.
从14.04开始提供更新的apt工具：
full-upgrade full-upgrade performs the function of upgrade but may also remove installed packages if that is required in order to resolve a package conflict.
在您的特定情况下，我看到，例如， linux-headers是一个由linux-headers-3.0.0-12和linux-headers-3.0.0-13提供的虚拟包，听起来像那种由dist-upgrade处理的软件包安装和删除，但不是通过upgrade 。
apt-get upgrade仅限于使用较新版本替换软件包的情况，但不需要添加或删除软件包。 例如，新版本的Firefox应该可以使用apt-get upgrade进行安装。
但是，当更新版本需要添加或删除时， apt-get upgrade将拒绝工作。 例如，当你安装内核linux-image-3.2.0-10-generic并且linux-image-3.2.0-11-generic出现时， linux-image-generic软件包会更新以取决于更新的版本。 要安装新内核，需要运行apt-get dist-upgrade 。
请注意apt-get upgrade如何表示内核包已被held back 。 这是使用apt-get dist-upgrade的提示。
基本上升级只会将现有软件包从一个版本升级到另一个版本。 它不会安装或删除软件包，即使需要升级其他软件包也是如此。 在内核更新的情况下，升级linux-generic软件包需要安装新的linux-3.0.0-13-generic软件包，并且由于升级拒绝安装或删除软件包，因此它拒绝升级linux-generic。
有时，程序包之间的各种不兼容性将需要删除一些程序包以升级其他程序包，这也需要dist-upgrade。 内核更新将始终需要dist-upgrade，因为它们的处理方式。 而不是让内核包得到更新，每次都会创建一个全新的内核包，内核元数据包会更新，以取决于新的内核包而不是旧内核包。 这样做是为了保留旧的内核版本，以便在引导新内核时出现问题，您可以从启动菜单中选择旧版本并进行恢复。
apt-get upgrade命令通常只安装当前安装的软件包的更新（或修复）。 例如，通常会使用此命令安装新版本的Mozilla Firefox 。
但是， apt-get upgrade通常不会安装新版本，其中需要进行重大更改（包括删除软件包或GRUB更新）。 例如，当一个新的Linux内核（linux-image-3.xx-xx-generic等）可用时，将不会安装该软件包。
要安装新内核，您需要运行apt-get dist-upgrade 。 当您运行apt-get upgrade ，您将收到通知，因为它会说某些软件包已被阻止。 这是你的使用提示： apt-get dist-upgrade 。