# Linux Directory Structure
> Let's learn about the Linux directory structure
>
> References: [howtogeek.com](https://www.howtogeek.com/117435/htg-explains-the-linux-directory-structure-explained/), [realforce111.tistory.com](https://github.com/chloe-codes1/TIL/blob/main/eng/Linux/Linux101/\[https:/realforce111.tistory.com/entry/%EB%A6%AC%EB%88%85%EC%8A%A4-%EB%94%94%EB%A0%89%ED%86%A0%EB%A6%AC-%EA%B5%AC%EC%A1%B0-%EB%B0%8F-%EA%B8%B0%EB%8A%A5]\(https:/realforce111.tistory.com/entry/%EB%A6%AC%EB%88%85%EC%8A%A4-%EB%94%94%EB%A0%89%ED%86%A0%EB%A6%AC-%EA%B5%AC%EC%A1%B0-%EB%B0%8F-%EA%B8%B0%EB%8A%A5\)/README.md), [coding-factory.tistory.com](https://coding-factory.tistory.com/499)
## Linux Directory Structure Diagram
* Linux is a Unix-based OS, so it uses many parts of Unix as-is
* In Unix, all **system**-related information and **hardware** devices are managed as files
* Like Unix, Linux also manages system-related information as files!
* Linux uses directories for efficient file management, organized in a **Tree structure** as shown above
* Directories are categorized by the **nature**, **content**, and **access permissions** of commands
* Most Linux distributions
* Use **FHS (Filesystem Hierarchy Standard)**, and
* Store files with the same purpose in the same location, so
* System resources and programs can be easily found
* In other words, commands / files / documents are managed in their own separate locations!
\
## Directory Structure
> I am currently using `Ubuntu 18.04`, one of the Linux distros, and the directory structure is as follows
### `/` - The Root Directory
* The **top-level** directory
* Must exist when setting up partitions!
* The directory that serves as the **reference for absolute paths**
### `/bin` - Essential User Binaries
* The directory containing Linux **basic commands (binaries)**
* Contains the essential commands needed for system operation
* Contains commands required for **booting**
* Also contains general commands that system users can use after booting
### `/boot` - Static Boot Files
* The directory containing **kernel images** and **boot information files** needed for system booting
* Contains the kernel boot image file specified in `/etc/lilo.conf`
* A very important directory during booting!
### `/cdrom` - Historical Mount Point for CD-ROMs
* Not included in the **FHS standard**, but can be found in distros including Ubuntu
* A temporary storage location for CD-ROMs
### `/dev` - Device Files
* The directory where device files are stored
* However, they are not actual files!
* It is a virtual file system that does not take up physical space
### `/etc` - Configuration Files
* The directory containing system configuration files
* **Network**-related configuration files
* **User** information / **password** information
* File system information
* **Security** files
* **System initialization** files and other important configuration files are located in this directory
### `/home` - Home Folders
* The location where system user home directories are created
* When a user account is created, a new user directory with the same name as the account is created as a subdirectory under `/home`!
* Since my Ubuntu only has one user `chloe`, the `/home` directory looks like this!
### `/lib` - Essential Shared Libraries
* The directory containing Library files that the binaries in `/bin` and `/sbin` folders depend on
* Libraries that the binaries in `/usr/bin` depend on are located in `/usr/lib`!
* Kernel module files exist in `/lib/modules`
* Most libraries are connected via links
### `/media` - Removable Media
* The directory for connecting external devices such as CD-ROMs and USB drives
### `/mnt` - Temporary Mount Points
* The directory for temporarily mounting file systems
* Generally used when mounting other devices
* Other directories can also be used!
### `/opt` - Optional Packages
* The directory where additional packages are installed
### `/proc` - Kernel & Process Files
* Stores various processor, program information, and hardware information of the system
* Like the `/dev` directory, it is a virtual file system that does not have physical capacity!
* It is not stored on the hard disk, but stored in memory by the kernel
* Shows the current system configuration
* You can check system information by using the **cat** command on files inside the `/proc` directory
* ex) Checking Interrupt information - `cat /proc/interrupts`
*
### `/root` - Root Home Directory
* The home directory of the root user
* Both `/` directory and `/root` are called root, but they are different!
### `/run` - Application State Files
* The directory where files related to running services are stored
### `/sbin` - System Administration Binaries
* Similar to the `/bin` directory, but contains executable commands related to system administration
* System check and recovery commands
* System initialization and shutdown commands, and other executable files needed for system administration exist here!
### `/srv` - Service Data
* The directory where data for services provided by the system such as FTP and Web are stored
### `/tmp` - Temporary Files
* Stores temporary data generated during system use
* Gets cleared during booting!
### `/usr` - User Binaries & Read-Only Data
* Contains most program library files for general users
* Basic **executable files**
* **Library files**
* **Header files** and other files are stored in this directory
### `/var` - Variable Data Files
* The directory where **data** and **logs (operation records)** generated during system operation are stored
* Stores dynamic files used by the system
* **Variable data storage directory**
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