我想知道为什么upgrade有时不想升级系统的某些部分，而dist-upgrade确实如此。这是运行后的示例apt-get upgrade：
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 …我通常在上学之前开始下载。
在完成特定任务后，我应该使用哪个命令来自动进行必要的保存并关闭计算机？
（例如，安装更新后，或下载大文件后。）
我也在unix.stackexchange 上交叉发布了这个。