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How a package system works.

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The method of software distribution found in the proprietary software industry usually entails buying

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a piece of installation media, such as?

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Such as an install disc or visiting each vendor's website and downloading the product and then running

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an installation wizard.

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So to install a new application on the system, right?

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But Linux doesn't work that way.

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Virtually all software for Linux system will be found on the internet and most of it will be provided

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by the distribution vendor in the form of package files and the rest of will be available in source

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code form that can be installed manually.

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And we will talk about how to install software by compiling source code in the next lecture.

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But first, let's get started with the package files.

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So the basic unit of software in a packaging system is the package file.

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A package file is a compressed collection of files that comprise the software package.

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So a package may consist of numerous programs and data files that supports the programs, and in addition

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to the files to be installed, the package file also includes metadata about the packages such as the

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text description or of the package and its contents.

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Right.

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So additionally, many packages contain pre and post installation scripts that perform configuration

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tasks before and after the package.

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Installation and package files are created by a person known as the package maintainer.

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Often, but not always an employee of the distribution vendor.

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Right.

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So the package maintainer gets the software in a source code form from the upstream provider or the

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author of the program compiles it and creates the package metadata and any necessary installation scripts.

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Often the package maintainer will apply modifications to the original source code to improve the program's

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integration with the other parts of the Linux distributions.

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We also have the repositories.

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Repositories here.

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Repo.

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The.

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Oh, race.

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While some shorter projects choose to perform their own packaging and distribution.

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And the most packages today are created by the distribution vendors and interested third parties and

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packages are made available to the users users of distribution in a central repository that may contain

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many thousands of packages, each specially built and maintained for the distribution.

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Right.

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So a distribution may maintain several different repositories for a different stages of the software

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development life cycle.

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For example, there will be usually be a testing repository that contains packages that have just been

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built and are intended for use by brave souls who are looking for bugs before the packages are released

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for general distribution.

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Right.

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And the distribution will often have a development repository where work in progress packages designed

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for inclusion in the distributions.

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Next major release are kept and it is revision may also have related third party repositories, and

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these are often needed to be supplied software for legal reasons such as patents or DRM anti-circumvention

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issues and cannot be included with the distribution.

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Perhaps the best known case is that of the encrypted DVD support, which is not legal in the United

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States, and the third party repositories operate in countries where the software, patents and Anti-circumvention

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labs do not apply, and these repositories are usually fully independent of the distributions they support

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and to use them, one must know about them and manually include them in the configuration files for

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package management system.

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And we also have dependencies the tendencies.

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Dependencies.

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So programs are seldom stand alone.

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Rather, they rely on the presence of other software components to get their work done.

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And common activities such as input output, for example, are handled by routines shared by many programs,

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and these routines are stored in a shared libraries which provide essential services to more than one

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program.

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And if a package requires a shared resource such as shared library, it is said to have a dependency.

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Modern package management system all provides some method of dependency resolution to ensure that when

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a package is installed, all of its dependencies are installed too.

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And we also have high and low package tools.

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And package management usually consists of two types of tools, which is actually let me write that

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down right here.

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So which is the low level, low level level.

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This is the low level tools that handle tasks such as installing and removing packages.

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And we also have high.

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Level.

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Tools, which is perform metadata, searching and dependency resolution.

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And in this section we will look at the tools supplied with the Debian style systems such as Ubuntu

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and many others and those used by Red Hat products.

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While older style distributions rely on the same low level program RPM, they use different high level

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tools for and for our discussion.

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We will cover the high level program such as UME used by Red Hat, Enterprise, Linux and CentOS and

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other Red Hat style distributions.

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Provide high level tools with the comparable features.