Understand Linux Fundamentals

0:12Hey, everyone, and welcome back to another skill.

0:15Within this skill here, we're going

0:17to look at how we can identify and locate

0:19system files and directories.

0:21Specifically, we're going to be taking a great interest

0:24in the /dev directory, as well as the /proc directory,

0:29and the /sys directory.

0:31Now, once we have explored our system files and directories,

0:34we're then going to pivot and then have a look

0:36at some of the user files and directories on the system.

0:40And then once we have done this, we're

0:41going to close by learning where we can find system binaries

0:45and programs within our directory structure.

0:48So really, we have a lot of very cool stuff

0:50to get to within this skill.

0:51Now, before we start, just to ensure

0:53that you are absolutely comfortable working at home,

0:56following along with this lab, what I just want to do

0:58is to highlight to you how you can quickly

0:59set up your terminal window to suit your needs.

1:02As you may see here, the output that I'm looking at

1:05is a little bit small.

1:07If I want to be able to adjust the font so it's

1:09nice and easy on my eyes, the way I can

1:11do this is that-- in fact, let me just close this

1:13down for a second here.

1:15I'll go down to the bottom left here.

1:16Just type in Terminal.

1:18Choose this one right here.

1:20I will have the Maximize icon.

1:21And then I'm going to go to this hamburger icon right here.

1:24If I then choose Preferences and I go down to Unnamed--

1:29that's just going to be my current profile--

1:30what I can do here is I can select a custom font

1:34and then click here.

1:35And basically, I can choose the font that I want.

1:38Let's maybe go into Ubuntu Mono, but I

1:40want the font to be bigger.

1:42So let me just arrow up [INAUDIBLE] get that bigger.

1:44If I then choose Select, we can see, here,

1:47immediately the text is bigger.

1:48If I want to change the color, I can uncheck the Use Colors

1:52from System theme.

1:54And then basically, I can choose the color that I want.

1:56So maybe I want to have black on white or gray on black.

2:00If you want to be a master robot-style hacker,

2:02you can do the green on black.

2:04Then all your text is now in green.

2:06So for now, all I'm going to do is

2:08I'm going to set my preferences as I'll

2:10have that white on black.

2:11And know that I'm happy and comfortable

2:13with my terminal setup, what I'm ready to do

2:15is to begin labbing.

2:17The very first thing that we're going to talk about

2:19is the basic pane-- something called the FHS.

2:22What on Earth is that?

2:23Well, that's what I'll be talking

2:24about in the very next Nugget.

2:25But for now, I hope this has been informative for you.

2:27I'd like to thank you for viewing.

0:12Hey, everyone, and welcome back.

0:14So in this Nugget right here, what I want to talk to

0:17you about is something called the Filesystem Hierarchy

0:21Standard, otherwise known as the FHS.

0:25So what exactly is the Filesystem Hierarchy Standard?

0:28Why do we want to know what this is and what it does for us?

0:31Well, the clue is in the name.

0:32It's all about how our file system is going to be laid out.

0:35It's going to be laid out-- any particular hierarchy.

0:38And this is something that is standardized.

0:41Now, I will say, standardized, in a kind of loose way.

0:44This is something that is not mandatory.

0:46Not all Linux systems have to implement the FHS.

0:50It's something that is looked at is more of a good practice,

0:53or maybe, should I say, general consensus.

0:56Quite simply, if you happen to boot up

0:58your Linux-based operating system,

1:00there is a high degree that the file system

1:02is going to follow this particular format.

1:04Now, you will see, in other Linux filesystems,

1:06additional directories, maybe things

1:08look a little bit different here and there.

1:10But very, very broadly these are the components

1:13that are going to make up the filesystem that you

1:16would interact with.

1:16So realistically, what we have to understand here

1:19is what exactly comprises of the Filesystem Hierarchy

1:22Standard, what of the directories involved here,

1:25and what is the purpose of each of those directories

1:27because the reality is they really are quite specific,

1:31which honestly makes sense the management much, much

1:33easier because once you learn what the Filesystem Hierarchy

1:36Standard is, you are pretty much going

1:38to know exactly where to go to solve the problem that you're

1:41looking for.

1:41Whether you're trying to mount a device within the file system

1:44or whether you want to happen to try to identify which devices

1:48are connected to your machine, knowing

1:50the layout of the filesystem is going

1:52to be very, very beneficial.

1:53Let me give you an example of one of the big distinctions

1:56of the Linux filesystem.

1:58Compare this to how it works on say, for example,

2:01a Windows-based system.

2:03Well, the file system is directly

2:05tied to the physical hard drive.

2:07What do I mean when I say that?

2:08Well, if you happen to come from a Windows-based system,

2:11you may happen to have a C drive as well as a D drive.

2:15Now, if you wanted to locate--

2:17say, for example-- the Downloads folder within your C drive,

2:20you would follow a very particular path.

2:21It would be something like-- say you go into the C drive,

2:24and then you go into the Users directory,

2:26and then you would have your user name, such as John,

2:29and then you would have your Downloads folder.

2:32Now, the crucial thing to note here

2:33is that this folder is explicitly

2:36within the boundaries of this physical drive.

2:39You see that?

2:39And similarly, if you went onto the D drive,

2:41you would have a same thing.

2:43Whatever path you ended up, that would belong

2:44to this particular drive.

2:46That is not necessarily the case when

2:48it comes to Linux directories.

2:50Instead, when you happen to navigate the Filesystem

2:53Hierarchy Standard, quite honestly,

2:55the physical hardware that is holding the data

2:57is completely abstracted away from you

3:00due to the way the disk may or may not be partitioned.

3:03You may go on to say, for example, the Downloads

3:06directory here.

3:07And you could be accessing data on one hard disk,

3:10and then you just change into another directory-- say,

3:12for example, the Documents directory,

3:14and suddenly you are accessing a completely different disk.

3:17Or maybe the Downloads directory and the Documents directory

3:21are on the same disk.

3:22The point is you can explicitly just

3:24tell, simply by looking at the directory path, so to speak,

3:28the same way you could on a a Windows-based system.

3:31So what I mean when I say that is if I go into Documents,

3:34I could be on one disk, whereas if I go into Downloads,

3:37I could be on a completely different disk.

3:39It is completely transparent to the end user.

3:42Now, there actually are particular ways,

3:43that we will get to see later on within this course--

3:46how to determine where exactly all the filesystems are

3:49physically mounted.

3:50But the point is is that you as the end user,

3:53just going about your job, day to day--

3:55it's all very smooth and transparent.

3:58So what we're going to do within this skill

4:00is we're really going to focus in on the structure

4:03of this standard.

4:04Now, one thing I just want to say

4:06is that if we happen to go back and I type in the command man

4:09hier and hit Enter, this is going

4:11to give me a very comprehensive summary of all

4:15the different endpoints that you can find within this directory

4:17structure.

4:18We can see, here, there are a ton of different options.

4:21What we have to understand, for the purposes

4:23of the examination, is not absolutely every single thing

4:26that you see here, thankfully.

4:27But there are some core components

4:28that we want to know about.

4:30Now, before we begin, one point that I just want to make really

4:33quite clear-- because it can be a little bit confusing if you

4:36are just getting started with Linux--

4:39we have this concept of the routes of the filesystem.

4:43Now, that is located at this particular point.

4:45If I do cd forward slash and hit Enter,

4:48now I'm in the root of the file system.

4:51We can actually see this here.

4:52There's a little forward slash icon in the prompt.

4:54And if I do an ls to list my directory structure,

4:58these are the components of the Filesystem Hierarchy Standard

5:01that we are going to focus in on.

5:02So this point here is the root file system.

5:06And as we're going to learn here,

5:07we also have this root directory.

5:10These are absolutely not the same thing at all.

5:13We will certainly get to talk about the differences

5:15later on within this skill.

5:17But really before we get going, just

5:19understand that this here-- what we're talking about--

5:22is at the root of the tree, meaning that everything

5:25that you see here all belongs within this directory here.

5:28So now that we've discussed the absolute basics

5:30around the Filesystem Hierarchy Standards

5:33and we have navigated to the root of the tree, how

5:36about we talk about the particular components

5:38that make up this Filesystem Hierarchy Standard.

5:41And the first thing that we want to be looking at

5:43relate to System Files and Directories.

5:45And well, that's we're going to be talking

5:47about in the very next Nugget.

5:48So I hope this has been informative for you,

5:50and I'd like to thank you for viewing.

0:00[AUDIO LOGO]

0:12Hey, everyone.

0:13And welcome back.

0:14Now, previously, we had just introduced

0:16some of the most basic concepts around the file system

0:19hierarchy standard.

0:20What we now want to do is to look

0:21at some of these system files and directories within the fsh.

0:25So with that said, let's dive in and begin.

0:29So as we know, we're at the very rich of a tree here.

0:32And we have all of these different directories

0:34to explore.

0:35The very first directory that I'm going to show you

0:38is going to be the boot directory.

0:40So if I do CD and go into boots, and hit Enter,

0:44this is where all the files, which

0:46are needed for your system to boots are located.

0:49So you're going to see things such as the kernel

0:51image, bootloader files, the initial RAM disk image,

0:54as well as files just relating to your kernel configuration.

0:57We can see here config 5.15.0.67.

1:00That here tells us the particular kernel version.

1:03And that is going to contain like, I say,

1:05particular configuration settings.

1:07Here, we can see the initrd, the initial RAM disk

1:10image for this particular kernel version, as well.

1:13Notice they match up right here and here.

1:15And the initial RAM disk is actually

1:17going to be used by the Linux kernel.

1:19When the system is putting up to allow

1:21us to load all the particular modules,

1:23it needs as well as all the associated drivers.

1:26Now, if we look at this particular directory here,

1:28grub.

1:29That contains all of the files needed by the grub bootloader.

1:33Now, we actually haven't discussed the grub bootloader

1:36quite just yet.

1:37But don't worry.

1:37We'll get to that very, very shortly.

1:39Just understand that it's just relating to the booting

1:42up of our system.

1:43And these particular files can be located

1:46within the boot directory.

1:48Now, we also see this vmlinuz.

1:50And that is linuz with a Z not an X.

1:53That's just basically your Linux kernel executable file.

1:56Once again, like I say, located within the boot directory.

1:59And one thing to note here is that when

2:01you happen to see a Z here, that actually

2:04tells you that this is the compressed version

2:06of the executable file.

2:07Whereas, if it says vmlinux with an X,

2:11that tells you that you have the uncompressed version.

2:14Just a bit of trivia in the case of,

2:16perhaps, maybe, say, an examination question.

2:18So without going into too much detail to early, the boot

2:21directory, like I say, this is just full

2:23of files needed to boot the system.

2:25The next directory I want to go to

2:27is I apply CD root to go back to the root of the tree.

2:29And I go into the eetc directory here.

2:32Quite simply, this is where your system's configuration files

2:36are located.

2:37We see a lot of dot confs here, for example.

2:39One thing to note here is that all of these blue files,

2:42we can see here, these happen to be

2:43directories, which contain even more subdirectories or files.

2:47And the white ones here are simply

2:49just the files themselves.

2:50So let's say I wanted to make some configuration

2:52changes to the networking on my system, where I would go

2:56would be into the etc directory.

2:58And then I could go into netplan.

3:00And then I can modify this particular YAML file.

3:03So right now, we can see here that my ethernet interface

3:06is effectively getting its IP address automatically

3:10via protocol known as DHCP.

3:12But if I so wish, I could specify a particular address,

3:15specify a particular gateway, or DNS servers.

3:19And like I say, this configuration change

3:21would happen within the etc directory.

3:24And there are way, way, way more examples than just

3:26simple network configurations.

3:28But let's move on.

3:29So the next directory is going to be the Lib

3:32directory at figure 1 here.

3:34Essentially, this is where all the important libraries

3:37that your system needs to operate are located.

3:40So we have libraries, such as apt,

3:42which is used for package management or cups,

3:44which is used to handle our printers.

3:46Or we can see here, we have libraries

3:49relating to the Python programming language.

3:51Or if we want to be able to listen to music on our system,

3:54we can use rhythm box, or perhaps

3:57work with some documents using libreoffice.

3:59All of these libraries are located right here in Lib.

4:03Now, the next one that I want to talk to you about, let's

4:06go back to the root of the tree, clear the screen.

4:09The one here is this one right at the very end, the VAR

4:13directory.

4:13So within the VAR directory, that

4:15is going to be the home of your variable data.

4:18Hence, the name VAR.

4:19Pretty much think about data that is ever changing.

4:22So data that is growing in size or shrinking in size, data that

4:26is not static.

4:27So think of things such as logs or perhaps maybe

4:30email, whatever it may be.

4:31So say, for example, you wanted to see

4:33the logs for the booting of your system, where would you go?

4:36Well, you would to look within the VAR directory.

4:39And then within there, we can see we have this log directory

4:43here.

4:43We can go into this.

4:44So we can see things such as the message right here.

4:47That is going to contain all of our kernel messages.

4:50So if I just say cat on that particular file,

4:52here is all this kernel information.

4:54And if we go on up to the very top,

4:56we can actually see the boot process began to kick off.

4:58As you can imagine, details such as logging,

5:00it's going to be variable.

5:01It's going to be changing.

5:03That is why it's going to be located within the VAR

5:06directory.

5:07So those are some of the common system files and directories

5:09that we have to understand for the purposes of Linux

5:12plus examination.

5:13But the reality is, there are even more on the system.

5:16Ones that we have to look at with a little bit more detail.

5:19The very next one that we're going to be looking at

5:21is the dev directory.

5:22And well, that's what we're talking

5:24about in the very next Nugget.

5:25But for now, I hope this has been informative for you.

5:28And I'd like to thank you for viewing.

0:12Hey, everyone, and welcome back.

0:14Now previously, we talked about some of the main system fails

0:17and directories within the file system hierarchy standard.

0:21We talked about the boot directory, as well as the etc

0:24directory, then the lib directory,

0:26and then finally, the var directory.

0:28Now, there are more directories within this domain

0:31to explore but like I say, they do perhaps require a little bit

0:34more attention to detail.

0:36And as such, I'm choosing to split them up.

0:38The one that we're going to be looking at in this Nugget right

0:41here is the dev directory.

0:44This is a super important directory, and the reason

0:46why is that this is where your device files are located.

0:51What exactly do I mean when I say device files?

0:54Basically, if you want your system

0:56to be able to talk to some hardware, maybe

0:59a keyboard or a USB drive, the system

1:02itself is going to use these particular device

1:05fails to make that connection happen.

1:08Unfortunately, it can't just happen with pure magic.

1:10The system is going to lean on and rely on these files

1:13to make this work.

1:14If we happen to go to this particular directory right now,

1:17we do a cd into the dev directory.

1:20If I do an ls, look at all this information

1:23that we see right here.

1:24So let me give you a breakdown on the types of things

1:27that you can expect to see right here.

1:28You can expect to see things such as sda.

1:32As it transpires on my machine right here,

1:34that's virtual machine happens to be

1:36running an ARM-based image because I

1:38am using Apple Silicon.

1:39And as such, this particular convention is not showing up.

1:43Instead here, the way it's showing on my system as vda

1:48but depending on what you are running at home.

1:50If you're running the ARM-based architecture,

1:51you can expect to see VGA, whereas if you happen

1:53to be running a regular virtual machine, very, very likely

1:57you're going to see this particular convention.

1:59But whether you see it or you don't, we

2:01do want to understand what that says because that is very, very

2:04common within Linux systems.

2:06Simply put, when you see sd, you can

2:10think of this as a hard drive.

2:12Now, and all the systems you would expect to see hd,

2:14but the reality is in modern systems

2:16are much more likely to see sd.

2:18Now, let me tell you what the convention actually is here

2:20because it really does tell you about the physical device that

2:24is connected.

2:25If you happen to see sda, the sd part

2:29tells that you are dealing with a hard drive

2:32and the a tells you that you're dealing

2:34with the first hard drive on the system.

2:37Now, if you happen to have an additional drive attached,

2:39you could see that shown up as sdb, b being the second drive.

2:44And if you had a third, that would be sdc.

2:48Now, that is not all.

2:49The way, we see here whereas in my case here,

2:51it is substituted for a V as opposed

2:54to an S. Notice that actually is a number as well, OK?

2:58So in the case here, I've got vda1, vda2, and vda3.

3:03You may have sda1, sda2, and let's just

3:08focus on these for now.

3:09So straight away, we know sd hard drive, a

3:12tells us this is the first hard drive.

3:14But look below that is the exact same right here.

3:16Both are the first disk.

3:18But the crucial thing here is that this one here

3:20tells us that says the first partition,

3:23and this number two here tells us this

3:25is the second partition.

3:27So let's imagine you happen to have two disks attached.

3:30The first disk would be disk a, the second one would be disk b.

3:34If they were partitions, let's see your hard partition 1 here

3:38and partition 2.

3:39And let's see, this one here had three partitions, one here

3:43and a split here.

3:44You have 1, 2, and 3.

3:47If I said to you, "Point out to me sdb3."

3:52You would know that is the second disk right here

3:55and it would be the third partition.

3:57That's part right here.

3:58You see that?

3:59Whereas if I say sda2, you would know

4:03that the a tells you is the first disk but as

4:05the second partition that I'm talking about.

4:08And' like I say, this information

4:10whereby you could derive these insights into your disks

4:13and partitions could be found within the dev directory.

4:16Now, the reality that is not all.

4:18You may notice a whole ton of these tty entries.

4:21These are just quite simply device fails denoting

4:24either a terminal or a console.

4:26If you happen to log in via a terminal,

4:29that will spin up as a tty session

4:31and it will appear here within the dev directory.

4:34Similarly, you may have to have a USB connected, in which case

4:38you will see the device file for that particular device

4:41and dev/usb.

4:45Now, the dev directory also has some special device files.

4:49And these special device files are used

4:51for very particular operations.

4:53The very first one that I want to draw your attention to

4:56is dev null, OK?

4:59Now, this as a special device file

5:01that is going to allow you to basically discard

5:03any information that gets put into it.

5:06What do I mean when I say that?

5:07Well, take for example, this right here.

5:09Let's say I wanted to look at the etc password fail, OK?

5:14Now, right now, that opens.

5:15No problem at all, let's clear the stream.

5:18Now, let's try one where I would get permission denied.

5:20If I tried to open say, for example, the shadow file.

5:23And don't worry if you do not know what these failures are

5:26quite just yet.

5:27Again, we'll talk about that later on within this course,

5:29certainly within great detail.

5:31But just understand, when I try to open this file,

5:33it's saying permission denied.

5:35Essentially, I would have to have superuser privileges

5:38to read this particular file.

5:39Same if I also try to open the sudoers file.

5:42Try that one.

5:43You see that?

5:44Now, if I try to count all these together,

5:45if I say cat etc password, and etc shadow, and etc sudoers,

5:52if I hit Enter, we open the first file but at the very end,

5:56we have these permission denied.

5:57So quite simply, we have two errors within our output.

6:01Now, if you happen to be dealing with a lot of data

6:03whereby maybe half of it is giving you

6:05errors and half of it is valid, being

6:07able to easily sort through that data

6:10so that you can effectively discard the erroneous data.

6:13What you can do is you can invoke that special file dev

6:17null.

6:17So let me show you what I mean.

6:19What I'm going to do is I'm going to take any errors

6:21and I can do this using this particular syntax as the number

6:24two, and then the forward arrow.

6:26And all the two means is that if I happen to have an error,

6:28I want to move the error into a particular location

6:33and I want to move it into dev null.

6:35If I now do this, look at this right here.

6:37Any of the erroneous output has essentially

6:40been dumped into the bin and we're only

6:42getting the outputs of the commands

6:44that we are successful.

6:45Now, that's a very, very simple and stripped down example.

6:48But honestly, the use of the dev null

6:50special file as extremely useful for system administration.

6:54And just to close, that also as another file known

6:58as /dev/random.

7:02This really is a special file that

7:04is going to allow you to generate random data that you

7:07can give off to applications.

7:08This can be very good if you happen

7:10to need some type of random data generator.

7:12Perhaps you're invoking some type of encryption, or maybe

7:15some random password generator.

7:17By invoking this particular special file within the dev

7:20directory, you can have easy access

7:23to that type of functionality.

7:24OK.

7:25So that is us for our introduction

7:27into the dev directory.

7:28Remember, this is where our device files are located.

7:31So whether we are connecting to a hard disk, or a USB drive,

7:34or a keyboard, these files right here

7:37are the files are going to facilitate

7:39these types of operations.

7:40So the next directory that we're going to be looking at

7:43is the directory.

7:44And well, that's what we're talking

7:45about in the very next Nugget.

7:46So I hope this has been informative for you,

7:48and I'd like to thank you for viewing.

0:00[AUDIO LOGO]

0:12Hey, everyone.

0:13And welcome back.

0:14Now, previously, we talked about the dev directory.

0:17And we learned that this is where

0:19our device files are kept.

0:21Now, what I want to do is I want to talk to you

0:23about the proc directory.

0:25How about we dive in and get right to it then?

0:28So the very first thing to note about the proc directory

0:31is that this as a virtual file system.

0:33And when I see it is a virtual file system,

0:36don't confuse that, as some people do,

0:37thinking that it doesn't really exist.

0:39It absolutely does exist.

0:41The difference is that it exists within memory.

0:44But basically, when you boot up your system

0:47within memory, dynamically on the fly,

0:50this directory here is going to be created.

0:53Now, the question is, what information does it actually

0:56hold?

0:56Well, quite simply, this is going

0:58to hold information relating to say, for example,

1:01you're running processes.

1:02It will also have information relating to say,

1:05for example, your hardware configuration,

1:07as well as providing details about options

1:09passed into the kernel.

1:10Now, the first thing that I want to do

1:12is to talk to you about these process numbers.

1:15So check this out.

1:16If I go to my terminal here, and I'm going to type in a command

1:19we have not visited yet.

1:20Once again, this is still early days.

1:22Don't worry about the details too much.

1:24Just seat back with a coffee and relax.

1:26All I'm going to do is say, pse.

1:29Now, when I do this right here, all I'm doing

1:31is I'm listing all of the processes on my system here.

1:34So if I scroll on up through all of these processes,

1:37at the very top, we have the systemd process.

1:39And to the left, we have this PID.

1:43This is the process ID.

1:44Basically, a numerical value associated

1:48with a particular process.

1:49Now, see all of these numbers here.

1:52If I happen to go into the proc directory,

1:55but I'm actually going to see something quite interesting.

1:58So let's do that.

1:58And we CD into proc.

2:00If I do an ls, we can see all of these files here and wait.

2:04But look at all of these numbers here in blue.

2:07These are all directories, which are

2:09associated with those processes that we just saw there.

2:13So within these directories, what we can find

2:16are particular files that are going to provide information

2:19about that particular process.

2:21So within say, for example, this directory here, 15,

2:25we will find information about how much memory

2:27is being used by process 15, as process 15 opening

2:31particular files, so on, and so forth.

2:33And, again, if you want to check what

2:34that process happens to be, we can say, pse, scroll on up.

2:38We recognize the process here as migration, for example.

2:41Go into the directory here and find all

2:43the correlating information.

2:45Now, one thing to really note here is that, like I say,

2:48this here is a file system running in memory.

2:50And it is being dynamically updated in real time.

2:54Say, for example, I happen to run the ping command.

2:57If I just run ping here, and I open up a new window,

3:00if I do a pse right now, at the very bottom,

3:04we can see here we have the ping process running.

3:06And it is associated with process 8229.

3:10So now, if I do an ls here, notice in my output here,

3:13I actually have this process 8229.

3:16Let me just stop this here, control-C.

3:18And I clear the screen.

3:20If I do an ls again, notice that particular process

3:24is no longer there.

3:258229 no longer here.

3:27That is because that process has stopped.

3:30I interrupted it.

3:31And because of that, the process ID

3:33is not actually appearing within this directory.

3:35Again, we can confirm, pse, no ping output at all here.

3:39So this directory here as being updated dynamically.

3:42Now, like I said, the information

3:44is not just about particular process IDs.

3:46We also have other information say,

3:48for example, our interrupts.

3:50If I do cat interrupts and I scroll on up,

3:54this particular file here is really

3:56good for locating problems where say,

3:58for example device drivers or hardware.

4:00Because you can essentially see here,

4:02how many interrupts are happening, which processes

4:04are causing interrupts.

4:06And all of this can essentially be

4:08related to performance issues on your machine.

4:11Not just that, if I just clear the screen, once again,

4:14within the proc directory, I could also get information on,

4:17let's say, the file systems here.

4:19What I'm seeing here are all of the file systems

4:22that are supported by the kernel the time running on my system

4:25right now.

4:26So I can see things, such as ext4, fat-based file systems.

4:30And once again, we are still very early.

4:31We'll talk about what all of these file systems

4:33are in an upcoming skill within this course.

4:36But understand, if we want to find that list of file systems

4:39that are supported by our kernel that we are running right now,

4:43we can find out within the proc directory within the files

4:46systems.

4:47Similarly, let's say, I wanted to get information

4:49about the memory usage of my system

4:52within the proc directory that will be a file called meminfo.

4:56If I open this up, check this out right here.

4:59Let me scroll on up.

4:59I can see my total memory.

5:01I can see the memory, which I have free, all of the buffering

5:04caching, so on, and so forth.

5:06All of that is also available within the proc directory.

5:09Maybe I want to see some type of information about my networking

5:13connections and my networking interfaces,

5:15but within the proc directory.

5:16We also have another directory known as the net directory.

5:21We can see this right here.

5:22If I do a CD net, or rather CD net, should

5:25I say, for doing ls.

5:26We have all of this information relating

5:28to say ipv6 routes, or simple network management protocol

5:33or routing information.

5:34All of these, once again, within the proc directory.

5:37Now, to be honest, there is an absolute ton

5:39of information within this particular directory.

5:41But for the purposes of the examination,

5:44you really want to be remembering

5:45that this is a virtual file system holding stuff

5:48like kernel information, hardware information,

5:50as well as information on those running processes.

5:54That is it for our introduction into the proc directory.

5:57We'll get to look at a lot of the information

5:59that we've sought here within this directory

6:01in a lot more detail later on within this course.

6:03But for now, the next thing that I want to talk to you about

6:06is the sys directory.

6:08And well, that's what we're talking

6:09about in the very next Nugget.

6:10So I hope this has been informative for you.

6:12And I'd like to thank you for viewing.

0:00[AUDIO LOGO]

0:11Hey, everyone.

0:13And welcome back.

0:14Now, previously, we talked about the proc directory,

0:17which we learned was a virtual file system created in memory.

0:20The next file system that I want to talk to you

0:22about is the sys file system.

0:25Once again, also a virtual file system,

0:28also created in memory on the fly.

0:31The question is, what exactly does this sys file system

0:33provide us in terms of information?

0:35Well, let's talk about it and find out then, shall we?

0:37The type of information we're going to find within the sys

0:40directory is going to be information relating

0:42to kernel modules, as well as hardware and driver

0:46information.

0:46And like I say, that is all going

0:48to be information that we can update

0:50on the fly and real time.

0:53Now, one thing I should just state

0:54as a point of clarification is that the file

0:57system itself is actually known as sysfs, so sys file system.

1:03The crucial thing to note here is

1:04that sysfs is actually just mounted from and accessible

1:08from the sys directory.

1:10So a little detail there, but important to understand.

1:13So let's go and have a quick peek

1:15into this particular directory, shall we?

1:17So let's CD into sys after doing ls.

1:21As we can see here, we have a number of directories.

1:24Now, if we go into the first directory,

1:25we're going to block devices.

1:27But then here, we can see some loopback information,

1:30as well as, in my case here, vda,

1:33which happens to be my desk.

1:34And just for posterity, if I just quickly go to the nodes,

1:38and I create an Ubuntu system, just

1:40give it a very basic setup.

1:42So I'll just copy this configuration here.

1:44And I will log in.

1:45Let's just accept the fingerprint,

1:47type in my password.

1:48So now, I'm on the cloud-based machine.

1:50No longer within my ARM architecture.

1:53If I go into the sys directory here,

1:55do an ls, if I go in to block devices,

1:57ls here, as we can see here, in this case here, as expected,

2:01we can see two disks, SDA, the first disk, and SDB.

2:06So any type of hard drives or solid state drives information

2:10about those drives will be found within the block directory

2:13within the sys directory.

2:15Whereas, if I go back out, let's maybe go into,

2:18let's say, the kernel directory within sys.

2:20Inside of here, we're going to be

2:22able to find things such as the kernel version or perhaps

2:25the kernel configuration, so on, and so forth.

2:27Similarly, if I go back, do an ls,

2:29if I go in to say, for example, devices, inside of here,

2:33I'm going to be able to find network information, computer

2:36information, memory information relating to all the devices

2:40that are connected to my system.

2:42So let me just exit out of the cloud right now.

2:44Go back to my own virtual machine

2:45right here, which I have locally on my computer.

2:48Let's maybe go into devices here.

2:50If I do an ls, I could go into the system directory.

2:53Do an ls here, I can see information

2:55relating to memory or CPU.

2:58Let's go into the memory directory here.

3:00If I do an ls, I can see my block size base.

3:04And if I cut this open, I can see the value here,

3:06which is a hexadecimal value, which

3:09I think, if I recall correctly, correlates to 128 megabytes.

3:14But don't quote me on that.

3:15The value itself is not important.

3:17The point is as the F, I want to get this type of information,

3:20such as memory block size information relating

3:22to my device.

3:24Well as expected, I can find that information directly

3:27within the sys file system.

3:29So the key point here to remember

3:30is that the sys file system, once again, just like proc,

3:33as a virtual file system created a memory and updated

3:37on the fly and real time.

3:38It's going to contain information relating to kernel

3:41modules, hardware such as block devices, devices,

3:44which are attached to your system,

3:45and information such as power management and the status

3:48of your battery.

3:49All of that type of information will be located

3:52within the sys directory.

3:53So I hope this have been informative for you.

3:55And I'd like to thank you for viewing.

0:00[AUDIO LOGO]

0:12Hey, everyone, and welcome back.

0:14Now previously, we had been focused on system files

0:17and directories within the file system hierarchy standard.

0:21Things like the boot directory or the lab directory.

0:23Or more recently, the dev, proc, SAS directories.

0:27What I now want to do, though, is

0:29to focus our attention more on the directories

0:32and files relating to users.

0:34So what exactly are the directories

0:36that we are going to focus on within this Nugget right here?

0:39Well, for a start, we'll be looking at the home directory,

0:42as well as the media directory.

0:45And then the mount directory, as well as the root directory.

0:50This is the one whereby there can be some confusion.

0:53And we'll also look at the TMP directory.

0:56So let's first begin by talking about the very first one

0:59at the very top here, the very well used home directory.

1:03So let's dive in and talk about them.

1:04OK.

1:05So if I do CD roots once again, I'm

1:08back to the root of the file system.

1:10If I go into this home directory right here,

1:13within this directory, there is going

1:15to be a directory automatically created with my username.

1:20So my username, as we can see here within the prompt,

1:22is IPvZero.

1:24If I do an LS, lo and behold, there

1:27is a directory here called IPvZero, after my username.

1:30And within that directory here, this

1:33is where I am in my home directory.

1:35And I can actually see here, within the prompt, this little

1:38tilde sign that actually lets you know that you're

1:41in your home directory.

1:43Now the purpose of this particular directory,

1:46is quite simply, this is your home.

1:47This is where you keep your own sample personal files.

1:51If I do an LS, we can see things such as documents.

1:54So if I've got some personal documents, such as my recipes,

1:58.txt.

2:00Maybe I've got some super simple but equally delicious

2:02pizza recipes, so pepperoni cheese and, I don't know,

2:07pizza dough.

2:07Well, I'm always quite lazy and just buy it.

2:10But there you go.

2:11Nevertheless, if I did happen to have my own recipe,

2:14will be storing that within my home directory

2:17and such a thing as my documents file.

2:19Of course, that is going to make much more sense

2:21than have that located in somewhere like, say,

2:23the boot directory.

2:24Similarly, we can also see within this directory,

2:27we have things such as our pictures.

2:29So if you happen to store any pictures,

2:31that should be a good directory for you.

2:33Or if you happen to have saved some videos, once again, this

2:38as the location you would want to save there.

2:40Now of course, there is nothing forcing

2:41you to follow this particular format.

2:44Indeed, if you decide, maybe I don't

2:45want to have a video directory, it's just a distraction for me,

2:49well, if I so wish, I can remove that.

2:52And if I do a listing now, suddenly that directory

2:54is gone.

2:55And maybe I would rather have a Linux study directory.

2:58Trying to be productive after all.

3:00The point here is that this is really

3:02a fully customizable workspace to meet your own needs.

3:05So as we move on, we go back to the roots of the tree.

3:09And we do a listing once again.

3:11We can see we have this media directory here.

3:14If we go in, we do an LS, we actually

3:16see nothing is in this directory.

3:18Now that is because this is going

3:20to be a location whereby you can mount and access

3:24removable media, things like DVDs or USBs,

3:27whatever it may be.

3:28That is going to be accessible within

3:31this particular directory.

3:32Now as it transpires, I don't actually

3:34have a USB connected to this device.

3:36After all, it is just a simple virtual machine.

3:38It's not a real machine.

3:39But I'm using it any real world way.

3:42But like I say, if you are running Linux in the real world

3:45and you do attach some type of USB stick,

3:48then the contents of that stick will

3:50be available via this particular directory.

3:52Now one thing I just want to point out to you,

3:55is that it might be a little bit confusing when

3:58you hear about having access to things like USB

4:01within the media directory because maybe you

4:04recall that we talked about a similar concept

4:06within the dev directory.

4:09Now the key distinction here is that the dev directory

4:13is where the device files for these devices are.

4:16So the files that actually facilitate these operations

4:20are located there.

4:21So if you attach a USB, the way that that

4:24can be essentially accessed was because a file

4:27was in the dev directory that facilitated that access.

4:30But once it has mounted and you actually

4:32want to access say, for example, the data on that USB,

4:36the media on that USB, the way you actually

4:39interact with that drive is going

4:40to be in the media directory.

4:43Now the next directory I want to show

4:44you is really, really similar once again but that

4:48has a distinction.

4:49So if we do an LS, we can see we have the mount directory.

4:52Now what we were just talking about with the media directory,

4:56we're saying how that can mount things like removable media,

5:00DVDs, USBs, and so on and so forth.

5:02So why on earth would we have a mount directory then?

5:06Well, the mount directory here is really for temporary mounts.

5:10And it really has a focus on temporarily mounting

5:13file systems.

5:14So if you happen to attach a file system that

5:17was mounted over the network, you

5:19would access that network drive via the mount directory.

5:24That is where you would want to mount that particular network

5:26share.

5:27Or perhaps if you wanted to access an external drive being

5:30used as a file system, again, you

5:32would want to mount that within the mount directory.

5:35Again, like I said, this is a temporary mounting point

5:37for file systems.

5:38It's going to be much more frequently used

5:40by technical people.

5:42Whereas the media directory, well, that

5:45is more used for the average user on the desktop.

5:48Say, for example, accessing media, mounting a DVD

5:51and watching it, say, for example.

5:53But these two can be quite confusing.

5:54But really try to draw a distinction here.

5:56One is really for accessing media.

5:58The other is just for temporarily

6:00mounting file systems.

6:01Now the next one is going to be, yep,

6:04maybe another confusing one, is going to be the root directory.

6:08Now you can see here, when I try to CD into this directory,

6:11it's telling me that the permission is denied.

6:14Maybe that will give you a clue as to what

6:15this directory is all about.

6:17Quite simply, the way we have this home directory here

6:21for the user IPvZero, well, the root account, i.e.

6:25the administrator of the system, also

6:27has this type of home workspace, so to speak.

6:30And the root directory is really just

6:33the root user's home directory.

6:34So if I want to be able to access

6:36this particular directory, what I would have to do

6:39would be to become the root user.

6:41So if I just log in as the administrator right here,

6:43notice now that I am the root user, I can say, who am I.

6:47We can see I am the root.

6:48If I do CD to take me to my home directory

6:51and I do a print working directory,

6:53we can see here that I am automatically now in the root

6:57directory right here.

6:58Now, this doesn't have the basic skeleton folder layout the way

7:01the home directory does, of documents, downloads,

7:03so on and so forth.

7:04But I as the root user, if I wanted

7:06to create such things, then of course,

7:08I could do that, no problem at all.

7:09I could just say, mkdir documents, do an LS.

7:12Suddenly I have that particular directory.

7:14So really this is just the workspace

7:16here for the root user.

7:18So let's go back and log in as my regular accounts.

7:21If I do a CD, I go back to my home directory.

7:25If I print the working directory, notice now

7:27I'm back within home IPvZero because as we see here,

7:30I am the user IPvZero once again.

7:32Now the last directory that I want

7:34to show you within this Nugget here

7:35is, if I go back to the root here

7:37and I now go into the TMP directory,

7:40now one thing to note here is that the TMP directory is

7:43colored a little bit different.

7:45Let me tell you this.

7:46The TMP directory is there for temporary files.

7:49And one of the caveats about this particular directory

7:52is that it has really, really relaxed permissions.

7:55Many directories, for example, will only

7:57allow you to read particular files within them.

7:59Some may even allow you to read and write particular files.

8:03But many will not allow you to actually execute

8:06particular files within them because of course, that

8:08could potentially be dangerous.

8:10The temporary directory though, is very, very relaxed

8:14in the respect that pretty much anyone can execute file

8:17from within this TMP directory.

8:19So after the file is located there,

8:21you can run it from there.

8:22So if I go into this directory here,

8:25all we're going to see here are a whole bunch

8:27of temporary files.

8:28And typically what would happen is

8:30that when you happen to reboot the system,

8:32the files here within this temporary directory

8:35are going to be deleted by particular startup scripts.

8:37It's not always the case, depending

8:39on the particular situation.

8:40But that is a very general behavior.

8:43And just one point to highlight about the potentially dangerous

8:46nature of this directory is that because

8:49of the relaxed permissions within this folder,

8:52this is often a folder utilized by hackers

8:54to break into a system.

8:56Because once they access this particular directory,

8:59they can actually have permission

9:01to run all these hacking scripts, such as bash

9:04scripts and Python scripts, to effectively attack and gain

9:07control of the system.

9:08So you've always got to be aware of that attack vector

9:11when managing your Linux system.

9:13Okidoke, so that is us for our basic introduction

9:16into the user files and directories

9:18on the Linux system.

9:19The next thing I want to talk to you

9:21about are these system binaries and programs.

9:23And well, that's what we're talking

9:24about in the very next Nugget.

9:26So I hope this has been informative for you.

9:27And I'd like to thank you for viewing.

0:12Hey, everyone, and welcome back.

0:14Now, previously, we looked at the file system hierarchy

0:17standard user files and directories.

0:19Now, what you want to do is to focus in on these system

0:22binaries and programs within the file system hierarchy standard.

0:26So the directories that we're going

0:27to focus in on in this Nugget is going

0:29to be the bin directory, the opt directory, as well as the sbin,

0:34and user directories.

0:36So let's dive in and explore them, shall we?

0:39So the very first directory that we're going to explore now

0:41is going to be that bin directory.

0:43So once again, we go to the roots.

0:45If we do an ls, we can see here it resides right here.

0:48If I do a cd bin and I do an ls here,

0:52you may think the output that you see

0:54here is really quite familiar.

0:56Let me show you what I mean.

0:57If I scroll on up, you might see things such as ls or scrolling

1:01or not be a little bit further, you

1:03might see things like cp or cat.

1:06Or one we looked at earlier, ps.

1:08Indeed, what we are actually looking at here

1:11are the binary executables needed

1:13for our system to operate.

1:15And you may notice that the color of all of the items

1:18here looks a little bit different

1:19instead of seeing blue for the directory, or white for a file.

1:24Instead, here I'm getting a whole bunch of green.

1:26That's because these are executable files.

1:28So the bin directory has all of these binary executables.

1:31But next directory we are going to look at

1:33is the opt directory.

1:34If I just go into cd, into the root, do an ls.

1:38Here is this directory here.

1:39Let's go in to see the opt.

1:41If I do an ls here, nothing is actually here at the moment.

1:45And that's because this is where you're

1:47going to find optional, hence the name, software

1:50packages that are not required that you

1:52could get via third party.

1:53Quite simply, this gives us a nice little space

1:56whereby we can isolate these programs

1:58from the rest of the system, thus making it really easy

2:01for them to be removed again.

2:02So if you want to build a third party program from source,

2:06this is where you want to be putting those files.

2:08Now, the next directory we're going to look at

2:10is going to be the sbin directory, which is right here.

2:14So if we cd into sbin, this looks really quite familiar.

2:17It's very, very similar to the bin directory.

2:20We're going to see these binary executables,

2:22need default our system to operate.

2:23But these are going to be system level binary executables.

2:27And typically, these are going to require

2:29privilege escalation, i.e. administrator access to utilize

2:33these from the sbin directory.

2:35And then lastly, the one we want to look at

2:37is the user directory.

2:39Now, within the user directory, there's

2:41going to be a whole bunch of subdirectories.

2:44And these are subdirectories are going to contain executables,

2:47much like we saw before as well, as directories

2:50for different libraries and documentation.

2:52So here's the thing.

2:53Remember, we saw our /bin directory,

2:57and within there we had all of those bin executables.

3:00Within our user directory, we also

3:03have another bin directory.

3:05And this is the bin directory used for local user programs.

3:09If I go into this directory here user bin this time, do an ls,

3:14we're going to see the same type of output that we saw before.

3:16But this is going to be, like I say, for local user programs.

3:19So again, you expect to see the same type of output

3:22if I happen to scroll on up.

3:24We can see things like the ls commands the pwd command,

3:27so on and so forth.

3:28And in fact, when I happen to go on to a system,

3:31let's go into my home directory, and I do an ls.

3:34Ultimately, what is happening is that under the hood, what

3:37is being executed is this command simply in shorthand.

3:41So if I do this right here, we essentially

3:43get a listing of the directory once again.

3:45Now, the reason why I don't have to specify the full path

3:48is because this particular path is set within a path

3:51environment variable.

3:53And if I just say echo$ same path,

3:55what we're going to see here are a whole bunch of directories

3:58separated by colons.

4:00So you see the first directory here,

4:02then the next one, then the next, so on and so forth.

4:05Quite simply, when I issue an ls,

4:08Linux automatically is going to check

4:10these particular directories looking for an ls executable.

4:14And if it finds it, then it's going

4:16to call it directly from that.

4:17So quite simply, we can just shorthand it

4:20and because of that path environment variable,

4:22Linus configure where the executable actually resides.

4:25So we'll get to make use of these executables

4:27in great depth through this course.

4:29But for now, that is us for our introduction

4:31into these system binaries and programs.

4:33So I hope this has been informative for you,

4:35and I'd like to thank you for viewing.