Someone who is habitual to Windows interface might find Linux very tricky !!
Where's my C drive ??? OR Where's the program files !
Where's the directory where Linux is installed ?
How to find anything ?
Once upon a time there was MSDOS - Disk Operating System. It was command line only but still you could play games and launch programs. You din't need Windows then.
Windows was added to PC and was installed on top of DOS.
You start the computer and just type Win to launch Windows.
It used letters to assign drives with a: & b: being removable disks since earlier PCs only had floppy drives. With the addition of hard drive. the letter c: became the letter for internal disk. Later Windows evolved their Kernel less and less dependent on DOS and eventually allowed Windows to boot without DOS at all. The Windows directory structure remained the same.
Now lets come to Linux.
Linux uses forward slash unlike Windows. Also Linux file and folder names are case sensitive. You can have multiple files within the same folder with same name but with different case probabilities.
All the Linux Distributions do not religiously follow the same structure but are all almost the same.
/bin & /sbin
Stands for Binaries.
Binaries are otherwise known as programs or applications.
ls to list files/folders in a directory, cat to read a file and other basic functions are stored here.
The latter stands for system Binaries.
This folder is exclusively for the system administrator and the standard user won't have permission.
Both these folders contain files which will accessible in single-user mode (root mode).
When you install programs in Linux there are not placed in these folders.
/boot
This is a folder you don't want to play around.
It has everything for your OS to boot.
Bootloader is within this directory.
/dev
This directory is for your hardware.
A disk for example will be /dev/sda.
The partition on that disk will be /dev/sda1, /dev/sda2 etc.
Your webcam, mouse, keyboard, printers all stay in this folder.
/etc
This is where all your configurations of your system are stored.
For example: /etc/apt has sources.list which has the list of repositories which your system connects to.
/etc/apt/apt.conf.d has all the settings of sources.
All your system-wide application settings across all the users lies here. For example libre office or your browsers will have user specific settings which will not be stored here.
/lib, /lib32 & /lib64
As the name suggests this is where the libraries are stored.
Libraries are files which are accessed by applications to perform various functions.
These are accessed by binaries in the /bin & /sbin folder.
/media & /mnt
This is where you would find other mounted drives.
Will have external hard drive, pendrive, network drive, RAM disk
/media is managed by the OS.
/mnt is when you manually mount a drive/network drive.
/opt
Called as the optional folder.
This where you would install additional software and applications.
/proc
/proc is where you would find sudo files.
The files in this directory has info about system processes and resources.
Every process will have a directory here which will have all information about that process.
Get the process id(PID) of any running process say for example 3112 and navigate to /proc/3112/
This folder is workable by developers.
cat /proc/cpuinfo will give you info about CPU.
Other ones you can try are:
cat /proc/uptime
/root
This is home directory for root user. Unlike a regular user's home directory it won't have the typical home directory folders in it.
/run
This is a new introduction.
This is a temp file system which runs in RAM.
When you reboot your system, it will become empty.
This folder is used by processes which is part of the boot procedure.
/snap
For installing snap packages which is a new concept of in Linux.
/srv
Service directory where service data is stored.
If you are hosting a FTP server or a webserver, here is where you will put files which will be accessed by external users.
/sys
Similar to /run directory. Used during the boot process.
It's a way to interact with the kernel.
It is written into the RAM and is created everytime the system boots up.
/tmp
A temp directory.
For example when you are using libre office, it wil regularly save a temp copy of what you are writing here. If the application crashes, you can look here for the most recent copy. Usually becomes empty when you reboot the system.
/usr
User application space.
Application which are user specific are installed here.
Any application installed here is considered non-essential for system operation.
Installed applications will stay in /usr/bin or /usr/sbin or /usr/local/bin or /usr/local/sbin and their libraries will be stored in /usr/lib.
Most programs installed from source code will end up in local folders.
/var
Variable directory.
It has files and directories which are expected to grow in size.
For example; /var/crash holds information about processes that has crashed.
/var/log will have log files of both system and many diff applications.
/home
Each user will have his own home folder.
Reference: https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.html