The difference of "apt-get update" and "apt-get upgrade"

apt-get update;apt-get upgrade;apt-get dist-upgrade各自的作用

apt-get command cheat sheet for Debian Linux

apt-get is the command-line tool for handling packages for Debian Linux which is use to:

Install/manage individual packages
Upgrade packages
Apply security patch(s)
Keep Debian system up to date
Download source .deb files
Front-end to many GUI and other utilities

Here is quick cheat sheet you will find handy while using apt-get at shell prompt:

Syntax	Description	Example(s)
apt-get install {package}	Install the new package. If package is installed then try to upgrade to latest version	apt-get install zip apt-get install lsof samba mysql-client
apt-get remove {package}	Remove/Delete an installed package except configuration files	apt-get remove zip
apt-get --purge remove {package}	Remove/Delete everything including configuration files	apt-get --purge remove mysql-server
apt-get update apt-get upgrade	Resynchronize the package index files and Upgrade the Debian Linux system including security update (Internet access required)	apt-get update apt-get upgrade
apt-get update apt-get dist-upgrade	Usually use to upgrade to Debian distribution. For example Woody to Sarge 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.	apt-get update apt-get dist-upgrade

{package} - Replace with actual package name





安装或升级系统分下面几个步骤。

第一步，获得最近的软件包的列表；列表中包含一些包的信息，比如这个包是否更新过。

第二步，如果这个包没有发布更新，就不管它；

如果发布了更新，就把包下载到电脑上，并安装。



apt-get update对应的就是第一步。

apt-get upgrade 与apt-get dist-upgrade对应的是第二步。



由于包与包之间存在各种依赖关系。upgrade只是简单的更新包，不管这些依赖，它不和添加包，或是删除包。而dist-upgrade可以根据依赖关系的变化，添加包，删除包。



一般在运行upgrade或dist-upgrade之间，要运行update.