# 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)

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## Linux Directory Structure Diagram

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* 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!

\ <br>

## Directory Structure

> I am currently using `Ubuntu 18.04`, one of the Linux distros, and the directory structure is as follows

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### `/` - The Root Directory

* The **top-level** directory
* Must exist when setting up partitions!
* The directory that serves as the **reference for absolute paths**

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### `/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

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### `/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!

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### `/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

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### `/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

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### `/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

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### `/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!

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### `/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

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### `/media` - Removable Media

* The directory for connecting external devices such as CD-ROMs and USB drives

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### `/mnt` - Temporary Mount Points

* The directory for temporarily mounting file systems
* Generally used when mounting other devices
  * Other directories can also be used!

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### `/opt` - Optional Packages

* The directory where additional packages are installed

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### `/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`
  *

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### `/root` - Root Home Directory

* The home directory of the root user
  * Both `/` directory and `/root` are called root, but they are different!

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### `/run` - Application State Files

* The directory where files related to running services are stored

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### `/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!

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### `/srv` - Service Data

* The directory where data for services provided by the system such as FTP and Web are stored

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### `/tmp` - Temporary Files

* Stores temporary data generated during system use
  * Gets cleared during booting!

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### `/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

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### `/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**