WEBVTT 00:01.330 --> 00:03.310 How a package system works. 00:03.580 --> 00:10.090 The method of software distribution found in the proprietary software industry usually entails buying 00:10.120 --> 00:12.280 a piece of installation media, such as? 00:12.490 --> 00:18.820 Such as an install disc or visiting each vendor's website and downloading the product and then running 00:18.820 --> 00:20.330 an installation wizard. 00:20.350 --> 00:23.130 So to install a new application on the system, right? 00:23.140 --> 00:26.300 But Linux doesn't work that way. 00:26.320 --> 00:32.800 Virtually all software for Linux system will be found on the internet and most of it will be provided 00:32.800 --> 00:37.930 by the distribution vendor in the form of package files and the rest of will be available in source 00:37.930 --> 00:40.840 code form that can be installed manually. 00:40.840 --> 00:45.670 And we will talk about how to install software by compiling source code in the next lecture. 00:45.670 --> 00:48.190 But first, let's get started with the package files. 00:48.840 --> 00:54.750 So the basic unit of software in a packaging system is the package file. 00:54.780 --> 00:59.010 A package file is a compressed collection of files that comprise the software package. 00:59.310 --> 01:05.310 So a package may consist of numerous programs and data files that supports the programs, and in addition 01:05.310 --> 01:11.790 to the files to be installed, the package file also includes metadata about the packages such as the 01:11.790 --> 01:15.480 text description or of the package and its contents. 01:15.480 --> 01:15.810 Right. 01:15.810 --> 01:23.460 So additionally, many packages contain pre and post installation scripts that perform configuration 01:23.460 --> 01:25.320 tasks before and after the package. 01:25.320 --> 01:31.110 Installation and package files are created by a person known as the package maintainer. 01:31.200 --> 01:34.890 Often, but not always an employee of the distribution vendor. 01:34.890 --> 01:35.220 Right. 01:35.220 --> 01:43.350 So the package maintainer gets the software in a source code form from the upstream provider or the 01:43.350 --> 01:50.980 author of the program compiles it and creates the package metadata and any necessary installation scripts. 01:51.010 --> 01:57.400 Often the package maintainer will apply modifications to the original source code to improve the program's 01:57.400 --> 02:00.820 integration with the other parts of the Linux distributions. 02:01.300 --> 02:05.390 We also have the repositories. 02:05.410 --> 02:08.800 Repositories here. 02:09.040 --> 02:10.480 Repo. 02:11.650 --> 02:11.980 The. 02:14.050 --> 02:15.520 Oh, race. 02:18.450 --> 02:23.760 While some shorter projects choose to perform their own packaging and distribution. 02:23.760 --> 02:29.610 And the most packages today are created by the distribution vendors and interested third parties and 02:29.610 --> 02:35.820 packages are made available to the users users of distribution in a central repository that may contain 02:35.820 --> 02:41.940 many thousands of packages, each specially built and maintained for the distribution. 02:41.940 --> 02:42.360 Right. 02:42.360 --> 02:47.970 So a distribution may maintain several different repositories for a different stages of the software 02:47.970 --> 02:49.270 development life cycle. 02:49.290 --> 02:57.150 For example, there will be usually be a testing repository that contains packages that have just been 02:57.150 --> 03:04.110 built and are intended for use by brave souls who are looking for bugs before the packages are released 03:04.110 --> 03:05.790 for general distribution. 03:05.790 --> 03:06.210 Right. 03:06.210 --> 03:12.900 And the distribution will often have a development repository where work in progress packages designed 03:12.900 --> 03:15.030 for inclusion in the distributions. 03:15.060 --> 03:21.760 Next major release are kept and it is revision may also have related third party repositories, and 03:21.760 --> 03:29.890 these are often needed to be supplied software for legal reasons such as patents or DRM anti-circumvention 03:29.890 --> 03:32.820 issues and cannot be included with the distribution. 03:32.890 --> 03:39.700 Perhaps the best known case is that of the encrypted DVD support, which is not legal in the United 03:39.700 --> 03:46.600 States, and the third party repositories operate in countries where the software, patents and Anti-circumvention 03:46.600 --> 03:53.410 labs do not apply, and these repositories are usually fully independent of the distributions they support 03:53.410 --> 04:01.390 and to use them, one must know about them and manually include them in the configuration files for 04:01.390 --> 04:03.580 package management system. 04:04.030 --> 04:09.490 And we also have dependencies the tendencies. 04:15.510 --> 04:16.340 Dependencies. 04:16.340 --> 04:19.630 So programs are seldom stand alone. 04:19.640 --> 04:25.760 Rather, they rely on the presence of other software components to get their work done. 04:25.760 --> 04:32.990 And common activities such as input output, for example, are handled by routines shared by many programs, 04:32.990 --> 04:38.210 and these routines are stored in a shared libraries which provide essential services to more than one 04:38.210 --> 04:38.870 program. 04:39.230 --> 04:47.430 And if a package requires a shared resource such as shared library, it is said to have a dependency. 04:47.450 --> 04:55.100 Modern package management system all provides some method of dependency resolution to ensure that when 04:55.100 --> 05:00.740 a package is installed, all of its dependencies are installed too. 05:01.010 --> 05:06.050 And we also have high and low package tools. 05:06.050 --> 05:12.260 And package management usually consists of two types of tools, which is actually let me write that 05:12.260 --> 05:13.340 down right here. 05:13.340 --> 05:18.600 So which is the low level, low level level. 05:19.170 --> 05:25.140 This is the low level tools that handle tasks such as installing and removing packages. 05:25.140 --> 05:27.480 And we also have high. 05:28.660 --> 05:29.590 Level. 05:31.720 --> 05:37.480 Tools, which is perform metadata, searching and dependency resolution. 05:37.480 --> 05:43.750 And in this section we will look at the tools supplied with the Debian style systems such as Ubuntu 05:43.750 --> 05:47.020 and many others and those used by Red Hat products. 05:47.020 --> 05:55.090 While older style distributions rely on the same low level program RPM, they use different high level 05:55.090 --> 05:58.210 tools for and for our discussion. 05:58.210 --> 06:07.690 We will cover the high level program such as UME used by Red Hat, Enterprise, Linux and CentOS and 06:07.690 --> 06:09.010 other Red Hat style distributions. 06:09.010 --> 06:12.070 Provide high level tools with the comparable features.