Repositories Overview
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Video Transcription
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>> Hey there Cybrarians and welcome back to
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the Linux Plus course here at Cybrary.
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I'm your instructor Rob Goelz.
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In today's lesson we're going to have
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an overview of repositories.
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Now upon completion of today's lesson,
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you're going to be able to understand what the purpose
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of a software repository is in Linux.
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We're going to find where
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repository files live in CentOS and Ubuntu.
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You're going to understand a little bit more about
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how a repository file is configured.
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Most Linux packages exist
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in something called a repository.
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That really is just a server
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that holds a collection of software,
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like a grocery store holds a collection of food.
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A Linux system gets the application and
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software updates from the repository server.
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But now you might be asking,
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how does Linux system know where
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these repositories and repository servers are?
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They use a repository file.
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In Red Hat, or Red Hat-based distros like CentOS,
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they keep a repository file or
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files in the etc/yum/repos.d directory.
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Debian-based distros like Ubuntu
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only have one file though,
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and that is found in etc/apt/sources.list.
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Now when you're looking at the structure of
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a repository file in CentOS,
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you have to be aware of seven different sections.
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This comes up particularly if you're getting
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into more advanced certification exams or Red Hat,
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you'll find that you're
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spending some time configuring these.
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Or if you're doing system administration
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on Red Hat-based systems,
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you're going to end up working in a repository file.
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The first thing you'll see is a section name and
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that is the name of the repository.
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It's enclosed in brackets.
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In here we see that this is actually the base OS.
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The next thing we see is the descriptive name
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of the repository.
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Then you're going to have a mirror list or URL,
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and that's just where you can actually find
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the repository out there on the Internet,
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a mirror list will be a list of
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different repositories that the system can use,
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ones download go to the next list in the mirror.
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You can see here that the base URL
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is commented out in favor of
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a mirror list so that
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there are a lot of different lists that it can hit.
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Right below we see GPG and GPG check equals one,
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and what that says is that the system is going to
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check the GPG signature of the repo.
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It's using that to ensure that
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>> the repository is correct,
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>> it has been signed by
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the people that create the software and when it's set
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to GPG check you also have the GPG key so
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that you can verify that that is correct.
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We have a path to the GPG
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or GPG key file right here at the bottom.
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Finally, we have an enabled field,
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and that determines whether or
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not the repo is going to be
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used as actively used on the system.
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If it's set to one,
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the repo will be used.
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But if it's set to zero, it'll be disabled,
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so one for enabled, zero for disabled.
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Now, for Ubuntu,
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it's generally just sufficient to know
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that Ubuntu has etc/app/sources.list,
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that's where it configures all of its repos,
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that's really all you need to know for Linux Plus exam.
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But a little bit more detail,
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each repo is going to have
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its own line in this file and there are four main repos.
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The main repo is for canonical supported software.
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The makers of Ubuntu,
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this is their software.
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Universe is going to be community maintain software.
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This is going to be things that are just
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out there in the community that you can use,
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but are officially supported by canonical.
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Restricted as proprietary drivers.
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Things are just used for devices.
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Then multiverse software that
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is restricted by copyright or legal issues,
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so you may be able to use these if
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you have the appropriate copyrights in place.
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But with that, in this lesson,
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we covered software repositories in Linux.
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We also talked about the CentOS and
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Ubuntu repo file locations,
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and we talked a little bit about the structure of
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repo files in CentOS and Ubuntu.
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Thanks so much for being here and I look
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forward to seeing you in the next lesson.
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