打包系统主要有两个阵营
包文件的简介
Package files are created by a person known as a package maintainer, often (but not always) an employee of the distribution vendor. The package maintainer gets the software in source code form from the upstream provider (the author of the program), compiles it, and creates the package metadata and any necessary installation scripts. Often, the package maintainer will apply modifications to the original source code to improve the program’s integration with the other parts of the Linux distribution.
资源库
While some software projects choose to perform their own packaging and distribution, most packages today are created by the distribution vendors and interested third parties. Packages are made available to the users of a distribution in central repositories that may contain many thousands of packages, each specially built and maintained for the distribution.
测试资源库
A distribution may maintain several different repositories for different stages of the software development life cycle. For example, there will usually be a “testing” repository that contains packages that have just been built and are intended for use by brave souls who are looking for bugs before they are released for general distribution. A distribution will often have a “development” repository where work-in-progress packages destined for inclusion in the distribution’s next major release are kept.
第三方资源库（法律原因）
A distribution may also have related third-party repositories. These are often needed to supply software that, for legal reasons such as patents or DRM anti-circumvention issues, cannot be included with the distribution. Perhaps the best known case is that of encrypted DVD support, which is not legal in the United States. The third-party repositories operate in countries where software patents and anti-circumvention laws do not apply. These repositories are usually wholly independent of the distribution they support and to use them, one must know about them and manually include them in the configuration files for the package management system.
依赖性
Programs seldom “standalone;” rather they rely on the presence of other software components to get their work done. Common activities, such as input/output for example, are handled by routines shared by many programs. These routines are stored in what are called shared libraries, which provide essential services to more than one program. If a package requires a shared resource such as a shared library, it is said to have a dependency. Modern package management systems all provide some method of dependency resolution to ensure that when a package is installed, all of its dependencies are installed, too.
上层和底层软件包工具
Package management systems usually consist of two types of tools: low-level tools which handle tasks such as installing and removing package files, and high-level tools that perform metadata searching and dependency resolution. In this chapter, we will look at the tools supplied with Debian-style systems (such as Ubuntu and many others) and those used by recent Red Hat products. While all Red Hat-style distributions rely on the same low-level program (rpm), they use different high-level tools. For our discussion, we will cover the high-level program yum, used by Fedora, Red Hat Enterprise Linux, and CentOS. Other Red Hat-style distributions provide high-level tools with comparable features.
Low level and high level
Packge Search Commands
如果下载了没有安装
注意这种方法没有解析依赖
上层工具卸载软件
一步更新所需的文件
软件包升级软件实现更新
显示现在有的软件
显示该软件的状态
获取软件包的信息
那个软件对该文件负责
