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File System Structure and its Description, we have

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file system in Linux that is divided into

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different directories, and that's something that

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we have seen previously as well. So, now I am

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going to take some time in this lecture to go over

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each file system partition or the folder or a

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directory that is set up in Linux, and I will

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explain you every directory in Linux file system

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and what is it used for. So, I have listed down

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all the directories and I will go over them,

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one by one based on how important they are. So

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the first one and the most important one that we

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have in the list is slash boot. Slash boot is the

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file or is the directory that contains files used

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for boot loader or the file that is in there is a

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grub.cfg, your configuration file. What

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happenes is every time your system boots up, the

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first thing the operating system that needs to

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boot up the system looks for slash boot and that

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is somehow hard coded in the disk, that you start

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up, go into slash boot, and you will find what you

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what operating system you need to start. There is

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old operating system or a new one or upgraded

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version. So it goes into the slash boot file, and

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it looks into it. By the way I will go over each

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one of the directory in my Linux system and I'll

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show you exactly what inside of each directory.

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Second one we have slash root, it is the root user

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home directory. Please remember it is not the same

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as slash. A lot of times people confuse slash

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which is also known as a root, but it is not

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actually slash root. So root when you log into a

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system or Linux system as root, and you do pwd, you

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will see you will be in a slash root, not just

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slash. Then we have slash dev directory. This is a

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systems device such as a disk, a CD ROM, speakers,

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flash drive, keyboard, any of those peripheral

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devices that are attached to your Linux system.

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They are created as a file as well and they will

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show up in a slash dev directory. Going and moving

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forward is the next one is slash etc, it is

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also one of the most important directory in Linux

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file system. It has all the configuration file. If

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you are running Sendmail, NFS, NTP, or any

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kind of application that actually runs on top of

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your Linux system, or that comes with a Linux

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system. All those configuration files are located

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in slash etc. If I wanted to modify something on

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let's say DNS, I will go into slash etc slash name.conf

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file. If I want to modify something in the Sendmail,

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I will go into etc, the mail, and sendmal.cnf,

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or that type of configuration file. So just

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remember that anytime you're making change in

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slash etc to any file inside of this directory

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please make sure you make a backup first of that

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file before you modify the configuration file.

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Then we have slash bin, slash bin in the newer

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version has been changed to slash user slash bin.

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It is like a linked to slash user slash bin and it

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is actually the directory where we have the

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commands that are used by everyday user commands

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like ls, pwd, these type of command, all of them

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are in slash user slash bin directory. Then we

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have another directory called slash sbin which is

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pointing or linked to slash user slash bin. This

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is a system slash file system commands. Those are

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the type of commands that you really need for

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system type of purposes. If you want to extend

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your file system or configure your file system

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that will take a look again, in our when I bring

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up my Linux machine, slash opt. slash opt is used

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for optional add-on application. It is not the

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application for operating system apps like NTP,

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DNS, those are the application that is actually

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come with the operating system. This slash opt is

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not used for those type of application that is

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used for third party application. Let's say if you

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are installing, let's say Oracle or some other kind

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of application or SCP, those are applications

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usually and most of the time are installed in

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slash opt.

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slash proc is the directory that is used

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in create files for all the running processes.

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Please remember when you shut down your Linux

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operating system there will be nothing in slash

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proc it will be empty. So, the kernel, which I

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will explain you later on what kernel is, but

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there is a program kernel in Linux that

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actually creates all these files for all the

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running programs in that directory once system

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shuts down, all those files go away. lib, which is

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now pointing to usr/lib, it's

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a location where all the C programming library

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files, and those files are needed for commands and

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applications. Meaning if you are running a

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command, let's say pwd or ls, all those commands

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actually do have a libraries attached to it that

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they could go and look for. And that's how these

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programs are run because they are written in C and

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C++. If you wanted to know which

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command is used, and sorry, which library file

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is used for which command, you could use this

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command strace -e open, like pwd is the

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command. That next one we have slash tmp

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directory, the directory that is used for

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temporary files. It has no significance

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whatsoever. But you could just if you want to

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create a file, a temporary file that you think you

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will delete later, you could create that slash

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tmp directory. Slash home directory is used for

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regular users while creating a regular account on a

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Linux file system, let's say iafzal, my home

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directory will be created in slash home. The next

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one we have is slash var. slash var is used for

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system logs. Every time your your operating system

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writes some output or some logs, all those logs or

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its application logs will always go into slash

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var. So if you are troubleshooting issues, you can

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always go into slash war log and other directories

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where you will find information about a specific

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application or if something going wrong with it.

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Then we have slash run, this is where the

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system's daemon starts up on very early stages. For

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example, systemd and udev to store temporary

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runtime files like pid, or process id files, and

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again, this will go away if the system is shut

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down, it just stores those process id and keeps

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track of it. Slash mount is used to mount external

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file system. If there is nothing, if nothing is

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mounted on your existing file system, then you

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could use that slash mount to create another

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subdirectory and mount any external NFS file

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system to it. Slash media is used for CD ROMs. If

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your system has a CD ROM drive and you put a CD

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ROM inside of it, then you close the tray. That CD

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ROM will be mounted under slash media. If you're

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using a virtual machine, you map the virtual drive

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to your virtual machine, that virtual ISO image

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will be shown under slash media CD ROM. So that's

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the list of all the directories that we have that

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support system structure and his description. And

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now I'm quickly gonna go into my Linux system and

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I'll show you exactly each one of them and how it

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is set up. So I am logged in as whoami, I'll do

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root, and I'll cd into slash, and I will do ls

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-ltr or ls -l, and you'll see all these

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directories that I have just covered. So first one

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I have is boot ,and if you notice in the boot there

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is these two directories grub and grub2. If I go

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into grub or grub2, let's go to grub2 and do

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ls -ltr, you'll see there is grub

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configuration file. This is the file that's

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telling the system which operating systems to

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start, or which version of operating systems to

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start. Let's go to slash root.

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This is the root home directory. If I just hit cd,

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and hit enter, and do pwd, this is the root home

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directory. There's nothing much in there. It's

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just its own Desktop, Document probably it has all

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of them are empty, nothing is in there. Then I

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will go to slash etc. This is the directory

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which has all the configuration file, most of the

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files that you're going to see in the in this

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directory or the subdirectories all of them will

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have conf. So it means it has configuration file

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going to slash bin which is pointing to use a bin.

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It has all the commands that we use, everyday

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command to actually talk to the operating system.

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Same thing with sbin This one has all the ones

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that deals primarily within your file system,

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disks, and extending the file systems. Then we have

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opt, you do ls -l. And you will see this is

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the one that is used for third party application.

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right now it only had like rh, which stands for

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Red Hat, nothing else. Then we have proc is the

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one that runs all the running programs

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temporarily, it is not the actual file that will

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stay on the disk. We have next one library, and

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library has all the library files that are needed

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to run a simple command. Next one, we have slash

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tmp, and slash tmp, you see all these are

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temporary files, you delete them, you create new

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files, it doesn't really matter. It's just a

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scratch space that you could put your files on.

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Then you have slash home. Slash home is for the

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users like I have my user here, I have another user

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called seinfeld, this is the home directory. Then

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the next one is slash var. Slash var is used for

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all the logs that are created in your system. So

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if you, primarily the main log is slash var slash

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log, and this is where all the logs are created,

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if something goes wrong with the system, this is

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where you have to come in. By the way, every one

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of these that I'm going through, I will go through again

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later on, and you will get more and more familiar

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with these file systems and it's directories, and

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all the commands that I'm running on. Then the

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next one we have slash run, this is the one that

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that runs the system daemons very early in the

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stages and is a temporary files. The next one we

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have mnt, this has probably nothing because I do

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not have any external file system mounted on my

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disk file, on my this computer. So if I mount it, I

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will use a command mount to file it and usually it

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gets mounted in slash mnt, because you have to

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specify it and that's where it goes. The last one

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is, we have slash media is, this is where if you had a

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CD Mount, CD ROM attached to your system, this is

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where it will go. Anyway, this is what I want to

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cover in the file system structure and

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description. I really hope that this lecture

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covers everything in terms of the file system and

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structure. Thank you.

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