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Hello, the beautiful people.

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Now, probably one of the most confusing things for new users of a GNU Linux operating system is understanding

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how to get new software now on other operating systems like Windows or Mac.

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Every time that you want to install a piece of software, you're probably just used to downloading an

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executable file, opening it, hitting next.

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Next, next, next.

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Next.

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A load of times avoid avoiding reading terms and conditions, but agreeing anyway and celebrating internally

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when your new software is installed.

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Now in Linux, it works a bit of a different way.

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I mean, you still celebrate internally when the software is installed, but you tend to install it

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in a way that is much more integrated, standardized, secure and scalable that is possible with the

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other operating systems.

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But to get those benefits from using a package manager, we first need to let go of our preconceptions

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from Windows and Mac and actually get a solid understanding of what is going on in Linux package management

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because it's not the same at all, but it is a lot better.

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So in this video you're going to learn about how to search for packages using APT by building off our

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existing knowledge of the software repositories.

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And we're going to show you how you can search those software repositories using the APT package manager.

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And you're also going to learn about how the app package manager uses caching to speed up performance

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and ensure that you have a fast installation experience.

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So by the end of this video, you're going to be able to know how to search the software repositories

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for new packages, and that's going to give you the fundamental understanding that you'll need in order

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to install them.

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So let's go ahead and get right into it.

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Okay.

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So as of now, we understand that there are a bunch of packages that exist and there will be using a

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package manager called APT to download and install them.

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So far so good.

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So let's start off by getting the APT program to search for packages.

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And let's say that we wanted to search for packages that will help us when working with Microsoft Word

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files.

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Now Microsoft Word files have conventionally had the extension dot, dock x, so let's find all the

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packages that are relevant to the text dock x.

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So to do that we would type the command apt dash cache OC Search Dock X and when we do that we see that

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we get a few results back with one package per line and we see that for each package we get the name

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of the package on the left.

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So you can see we've got one here called Dock X to two text.

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We've got one here called Lib, Apache and so on.

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And then on the right we get a short description about that package.

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So this will turn Microsoft s XML files to plain text, and this one is a general markup converter and

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it's the libraries for that general markup converter.

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So you can see at a glance what, what is available.

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And for example, if we wanted to search for things to do with text, we could always use grep and search

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for the word text and we would get just a few results there.

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So you can also narrow this down using grep.

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Okay.

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So it appears here that we may be interested in this one here called dock x to txt.

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Okay.

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So how would we get a bit more information about that?

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What we could do if we clear the screen is do is use apt cash show dock x to text.

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So instead of apt cast search and then a keyword, we're going to use apt cash show and then the package

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name.

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And when we enter that, you can see that we get a whole bunch of information about that package.

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Now this is exactly the kind of information that's good to pipe through the less command to make it

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a bit easier to deal with.

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There we go so we can see the package name is Dock X to txt.

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It's available for all architectures.

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It gives you the version number and it also tells you where it's from.

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So it's from the universe repository, the text section in there.

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It tells you the maintainers with their contact information tells you where to report any bugs and it

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tells you loads of other stuff.

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But down here there's also a description and it says it converts Microsoft XML files to plain text and

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it gives you more information.

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Doc Doctor TXT is a tool that attempts to generate equivalent ASCII text files from the Microsoft Doc

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X documents.

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Okay.

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And you can read that if you wish.

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Okay.

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So you can see by using apt cash show, we can see plenty of information about the doc x to text package.

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So that's a really useful ability there.

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Now let me show you something.

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So we've done all that with access to the Internet, right?

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So if I click up here, you can see that I've got a connected Internet connection.

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Well, let me try and disconnect my virtual machine from the Internet and try that again.

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So I'm going to turn off my connection.

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And you can see now I've got no Internet connection whatsoever.

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If I open up Firefox and we'll probably see it, tell us that there's no internet connection.

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If I go to somewhere like, I don't know, let's say YouTube.com, it'll tell me that the server's not

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found, okay?

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Because there's no Internet connection.

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So with that, let's try and do it again.

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Okay.

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Let's search for the term web server.

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So if I do apt cache search and I want the term web server because there's, because there's two words

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in here, I'm going to enclose them in quotes here.

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So they go as one search term rather than two separate search terms.

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If I didn't have quotes and I did web server, it says If I search for web on its own and then server

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on its own, but I want to search for web server together.

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Okay, so apt cache search.

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And you see we get actually a whole bunch of results.

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So let me clear the screen and pipe that through less to make it a bit easier to handle.

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But actually.

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Wait a second.

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Isn't that quite strange?

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How was apt able to search for all these packages without having any internet connection?

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Hmm.

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And there appears to be a package here called Apache two that gives us the very popular Apache Web server.

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Okay, so let's try and get more information about that.

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So it's called Apache two.

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Let's do apt cash show Apache two and pipe that through less just to make it a bit easier to read.

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And yeah, we managed to get information about that, how strange it was to even get detailed information

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about the package.

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So how is that possible if we don't have an Internet connection?

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Well, if the information is not stored on the Internet and it's not being downloaded from the Internet,

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then it must be stored somewhere on this computer.

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And it is.

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So this information is stored in something called a cache.

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Now, what's a cache?

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Well, having come across, you may have come across the word cache when browsing websites and you know

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when your browser gets a bit slow.

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So you decide to clear out your browser's cache to speed up performance.

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But what is a cache?

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Exactly what a cache is a kind of storage place for information that's supposed to be efficient and

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easy to access.

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To explain this, let me tell you a little story.

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So let's say that you wanted to keep looking at a certain website and it was called w-w-what awesome

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site dot com.

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Now without a cache, every time that you wanted to visit awesome site, your computer would send a

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request all the way across the Internet to a computer known as a web server that holds all the files

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for w-w-what or sitcom.

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And this web server could potentially be across the other side of the world.

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And sending messages back and forth can take some time.

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But let's say that you visit awesome site and your computer sends a message all the way to the web server

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that happens to be on the other side of the world.

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After its long journey, your request arrives and it waits patiently in line behind all of the other

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requests that have arrived there first.

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So after dealing with all the other requests and that have come before you in the queue, the web server

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will ask, How can I help?

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And your request would say, Can you give me a copy of your home page, please?

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And the web server would reply.

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Sure.

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Let me find it for you.

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It's such as ran for a little while and then goes, Oh, here you go, and transmits bit by bit a copy

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of that file all the way back to your computer, over the internet, across the entire world.

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Now, you can imagine the whole process might take a bit of time, wouldn't it?

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Now, without a cache, the next time that you want to access WWE or some sitcom, the same thing happens

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all over again.

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Your request travels to the side of the world, wait in line and the file is sent bit by bit all the

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way back across the world.

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And this happens again and again and again.

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Now, imagine that it's not just you, but thousands or even millions of people all at the same time

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requesting awesome sitcom.

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I mean, it is awesome, after all.

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And if everyone in the world has to do the same process over and over and over again, you can imagine

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that the web server might start to become a bit overburdened.

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The queues get really long.

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There's a backup on the data highway and your web experience just slows way down.

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So to fix this problem, that's where a cache comes in.

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That's why cache is come in.

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Okay.

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So instead of being sort of the only being one copy of the file stored on the web server instead the

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very first time your request comes back, your it will keep a copy on the local computer in what's called

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a cache.

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Now the cache is nothing more than a place to store files locally so that you get performance benefits

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later.

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Now, the second time that you want to visit, visit, awesome site, your computer doesn't need to

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shoot messages all over the internet.

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It realizes that awesome sitcoms files are already in your cache, and then it just looks in the cache

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on your computer locally and loads the page, which is much, much faster.

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Now the only issue is that the cache must be kept up to date with what's on the actual web server.

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Otherwise you'll keep viewing an outdated copy of the files.

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So that's what a cache is.

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Now that we understand what a cache is, we now understand the reason why the command is called apt

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cache.

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And when we run apt cache search, what we're doing is we're telling the app package manager to look

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inside the cache for any packages matching the text that you give it.

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So if we did apt cache search text, it's looking inside its cache for all packages that match the word

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text.

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And if we run apt cache show Apache two, it's going to look for the Apache two package in its cache

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and bring up all the information that it's got about it.

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So where is this cache then?

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Well, on ubuntu the cache is located at slash var slash apt slash lists.

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So if we seed into there, let's go ahead and take a look.

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Okay, slash var slash, apt slash, sorry, slash, var slash lib slash apt slash lists.

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Okay, so now we're in there.

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If we take a look, we can see there's a whole bunch of different lists in here.

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Let me just list them out into the last command and we can see that we've got a whole bunch of files

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in here that are actually just lists of packages.

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Now, these are the lists of all the packages available from.

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The repositories that have enabled on my system and the lists also cover specific type of packages.

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Let me let me clear the screen and let me just maximize it as well and list it out again.

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But piping it through the last command with the capital end option.

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And this allows us to have some line numbering which will make it a bit easier to explain what I'm talking

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about.

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So here we are.

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We've now got each of the lines with some line numbering.

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Now you can see that there's so many different lists in this folder, each with a specific, each containing

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list of a specific type of package, depending upon where it came from and what type of computer architecture

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it's for.

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Now, a lot of mine start with the GB dot archive ubuntu dot com.

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Now that's because my nearest Ubuntu archive server will be in the UK because I'm based from the UK.

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Okay.

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In GB is for Great Britain and because I'm in the UK, that's where it sends its requests because it's

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a bit more efficient to send your requests to a server that's closer to you.

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But yours might be different depending upon where you are in the world.

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Okay, so if you're in the US it might say something like US, dot archive, dot com and so on.

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So don't worry about not having GB there.

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Everything else should be more or less the same though.

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Now on line three, there's a list of available artful packages.

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So for the artful code name version of Ubuntu, you can see that we've got the binary packages.

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So the pre compiled packages that are for the AMD 64 computer architecture from the main repository.

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Okay.

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And if we take a look online 15, we can see that we've got again for the artful version, we've got

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the binary pre compiled packages for the AMD 64 computer architecture, so 64 bit architecture with

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from the restricted repository.

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And you can see here we've got some from multiverse and so on.

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So the lists are broken up very specifically by where they came from and what they're for.

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Okay.

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Now these are not the packages that are installed on my computer, but they are the packages that are

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available in the software repositories that I've chosen to access.

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So these I don't like these aren't lists of packages that I have installed, but are lists of packages

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that I could install from the software repositories.

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Okay.

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So let's take a just take a quick look at one of these files that ends at entry.

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Okay.

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So let's say that we want to edit the entry for the GCC package that we downloaded a couple of videos

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ago.

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Well, we know that it's going to be in the main repository because it's open source and it's free software,

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but it's not maintained by the community.

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So we know that GCC should be the main repository.

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We also know that it's pre compiled and it's therefore a binary package.

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We didn't have to download GTC and then compile it.

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We just installed it straight away in the last few videos, which means it's pre compiled.

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So if we look for the list that we see, that's for art for main directory, main repository with a

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preconfigured preconfigured 64 bit binaries.

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Now let's have a look for that.

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So we've got artful and we see four main here we are main binary AMD 64.

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So it should be in this list.

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So if I just copy that and I add this and I open that up with Nano, so I do nano and paste that if

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I can.

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There we go.

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So now if I press enter, you can see that we've opened the list and we've got a whole bunch of different

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packages in here.

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And you can see that this is starting to look like the results from APT Cash Show and that's exactly

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what happens.

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That cache show will just search through the files and print out the the information regarding that

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package.

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So now that we're in this file, why don't we just go ahead and search for the package called DCC?

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So the way we can find that a bit easier, instead of just searching for GCC, you can notice that the

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actual package bit starts with the word package, then a colon, then a space, then the actual package

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name.

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So let's try and do that for GCC.

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So we're going to do package colon space, GCC.

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And if I press enter, we'll see that we've ended up at the GCC package and you can see that we get

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all the information about the GCC package that we installed a few minutes ago.

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Okay.

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In the last video or so and it comes up.

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So let's change the priority from saying optional here to saying optional, but awesome.

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Okay.

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So if I if I save that right, that file opens it same permission denied because this is a special file

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we need to open it with sudo.

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Okay.

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So it's open it with sudo nano where you can do that as just press the up arrow key, then type sudo

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at the beginning and enter your password.

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Then we're going to search for package package colon DCC.

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There we are.

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Then instead of having it say optional, we're going to have it say optional, but awesome with an exclamation

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mark.

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Of course, save the file and exit.

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Okay, now, if we just close the terminal and open it up again.

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Okay, now if we do apt cash show GCC and maximize the term a little bit and pipe that through less.

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We can see here that it's pulled the information for GCSE and now the priority is optional but awesome,

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which is fantastic.

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Okay, how cool is that?

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So you can see here that what's actually happening is you've got a cache, a I guess a place, a folder

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on your computer that stores lists that your package manager can search through regardless of whether

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you've got Internet connection or not.

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And that is located at slash, var, slash, lib, slap, slash, apt slash lists.

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So if we go, that's a massive difficulty to say if you're looking there, you've got all these different

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lists, each for specific purposes.

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And because we wanted to look for the GCC package, we used a little bit of our understanding of repositories

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to understand that the GCSE package would be located in the main repository because it's, it's probably

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it's maintained by Canonical because it's so old you see, and you've got the, it's pre compiled,

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it's ready to go so it's going to be binary and we are on an amd64 computer architecture.

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So that's the list that we're looking at.

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So we kind of took this, this file here, this file name which is very long, but it's a file name

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nonetheless.

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And we took a look at it with Nano and we opened it up and we are, oops, I need to enter my password.

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So we opened it up and we saw that this is where when you try to show more information about a package,

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the package manager gets this information and we looked for the GCC package, okay?

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And we found out that this is where it is.

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And then we edited some of that information to demonstrate that this is exactly where the information

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is coming from.

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So if we now look at APT cash show GCSE, we can see that now that information is no longer optional,

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but awesome, but it's just optional.

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So now you can see a bit behind the scenes how your package manager is working.

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So now we understand that for performance benefits, Aptx saves a cache of all available among two packages

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on your local system in the slash via slash lib slash apt slash lists directory, and that's called

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the apt cash.

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That folder is called the APT Cash and by searching the APT cash using APT cash search and that a search

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term apt will search all of the lists in those in that cash in that folder for any package names that

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have something to do with that search term.

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So it'll search the package name and the package description in all of those lists and return to you

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the package names with a little snippet, a little description of each package, so that you can look

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for more information if you want.

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And you would look for more information using APT Cash show and then the package name that APT Cash

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search would give you back.

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And this will show you detailed information about the package.

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Okay.

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Things for anything from the size of it to a description to what it does, who the maintainers are,

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where to report bugs and everything that you could possibly know about that package.

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Now, all of this is done using lists that are installed in the cache.

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So lists are downloaded to the slash via slash lib slash apt slash lists folder.

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And all of those files in there are just lists of packages and they all have basically the same format,

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but that's where everything is saved and it just uses the lists in that folder to produce all this functionality.

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But this makes us wonder how did the lists actually get into the cache in the first place?

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And just like any cache, it must be kept up to date, otherwise new packages could be released and

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you wouldn't know.

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So how do we keep the cache up to date?

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Well, you're in luck.

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These questions and many more will be answered in the next video.