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# Functional Structure
The *Linux* operating system is **structured** in a tree-like form and follows the Filesystem Hierarchy Standard (FHS). The main file system folders that compose the structure can be represented in the following diagram:
## Common Directories
Some common directories in a *Linux* filesystem that play key roles in system configuration, file storage, operational functions, and performance are:
* ***`/`*****:** The root filesystem, where all of the files required to boot Linux are stored
* ***`/etc`*****:** Store configuration files that are used by the operating system
* ***`/etc/bash.bashrc`*****:** Script that contains bash settings
* ***`/etc/passwd`*****:** List of all user accounts
* ***`/etc/issue`*****:** Usually contains information about the OS
* ***`/etc/crontab`*****:** Contains the cron jobs that are executed by the system
* ***`/etc/shadow`*****:** Contains encrypted information about credentials
* ***`/var`*****:** Store data that is frequently accessed or written by services or applications running on the system
* ***`/var/www/html`*****:** Default store for the server root folder
* ***`/root`*****:** Home directory of the root system user
* ***`/tmp`*****:** Temporary files that store data that is only needed to be accessed once or twice. Once the computer is restarted, the content of this folder is cleared out
* ***`/opt`*****:** Stands for optional, normally third-party software information
* ***`/bin`*****:** Basic programs of Unix (binaries)
* ***`/sbin`*****:** Binary programs for system administration
* ***`/usr`*****:** Contain users' information
* ***`/usr/bin`*****:** Installed packages and applications
* ***`/usr/share`*****:** Application support and data files
* ***`/proc`*****:** Contains information about internal jobs and processes of the system
* ***`/proc/version`*****:** Information about OS
* ***`/media`*****:** Where external devices are mounted
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