Linux File Hierarchy

Introduction

• Linux File Hierarchy Structure (FHS) : It's like a map that tells us where everything goes in a Linux computer.

• Maintained by Linux Foundation : The FHS is managed by the Linux Foundation, which makes sure everything stays organized.

• Root Directory (/) : This is the main place where all files and folders start from, no matter where they are stored.

• Universal Usage : Most of these directories are used the same way in all UNIX systems, but the FHS gives specific details for Linux systems.

1. / (root) :

   • The computer system's root directory serves as the head of every folder.

   • Beginning with this root directory, which is simply a forward slash (/), all files and folders are created.

   • This directory is only directly editable by the root user, who is the boss.

   • The root directory (/) is not where the administrator stores private files. /root is the boss's personal folder; it is not the same as the root directory (/).

2. /home :

   • Each user on a computer system has a personalized place thanks to home directories.

   • Users save their own files, preferences, and other private information in their home directories.

   • Every user can freely handle their files in their own home directory, such as /home/chandra or /home/prakash.

   • Home directories limit access to each user's files and preferences, protecting privacy and security.

3. /usr :

   • This level includes the majority of user utilities and apps as well as read-only user data.

   • For programs at the secondary level, it contains source code, libraries, documentation, and binaries.

   • Key directories for user programs include :

     • /usr/bin: Holds binary files for user programs like at, awk, cc, less, and scp.

     • /usr/sbin: Contains binary files for system administrators such as atd, cron, sshd, useradd, and userdel.

     • /usr/lib: Stores libraries for programs in /usr/bin and /usr/sbin.

   • User-installed programs are typically found in:

     • /usr/local: This directory houses user-installed programs, typically installed from source code. For example, Apache web server installations go under /usr/local/apache2.

   • Key system resources, such as header files, the Linux kernel code, and documentation, can be found in:

     • /usr/src: Documentation, header files, and Linux kernel sources are all contained in this directory.

4. /etc :

   • These are unique files that impact the entire system and are unique to the computer they are on.

   • They contain crucial configurations that are required by every installed program on the system.

   • Scripts that manage how apps launch and terminate at computer startup and shutdown are also located in this directory.

   • Some examples include /etc/resolv.conf, which stores DNS server settings, and /etc/logrotate.conf, which configures log rotation settings.

5. /root :

   • The root user, who has complete authority over the system, keeps this directory private.

   • This directory's contents can only be accessed and changed by the root user.

   • It functions as a secret space where the root user stores and manages sensitive system configurations and files.

   • It is not the same as the top-level directory for the entire file system, the root directory (/).

6. /opt :

   • These are additional software applications that you may or may not need, but that you may like to install for particular uses or purposes.

   • Several apps that are not part of the operating system are stored in this directory and come from different sources.

   • Installing add-on programs should take place in a subdirectory of /opt/ or directly under the /opt/ directory. They remain divided from the main system files as a result.

7. /lib :

   • Important libraries that are required for the correct operation of programs in /bin/ and /sbin/ are kept in this directory.

   • This directory contains libraries that are essential to running programs from /bin/ and /sbin/.

   • Library filenames typically start with "ld*" or "lib*.so.*".

8. /boot :

   • The files in this directory are necessary for the operating system to boot up.

   • These are the files, such as kernels and initial RAM disk (.initrd) files, required by the boot loader.

   • Here are some important files: GRUB, vmlinux, and kernel initrd.

   • Bootloader :

     • A bootloader is a brief software application that launches with your machine. It is the first application to launch when the system boots up.

     • Locating and loading the operating system into memory is its primary duty. It finds the kernel and necessary files for the operating system to boot up.

     • In addition, the bootloader manages hardware initialization, making sure that all necessary hardware parts are set up correctly before the operating system takes over.

     • A boot menu is provided by certain bootloaders, such GRUB (GRand Unified Bootloader). Users have freedom at starting by being able to select from a variety of operating systems or boot settings via this menu. Because it enables users to boot into several operating systems that are installed on the computer, GRUB is especially flexible.

     • Other bootloaders such as LILO, Syslinux, rEFInd, and UEFI exist in addition to GRUB. With a range of features and functionalities, each responds to particular needs and tastes.

9. /sbin :

   • The system binaries included in this directory are essential for system maintenance and operation.

   • Just like the /bin directory, /sbin also stores binary executable files.

   • System administrators usually use these commands to perform routine maintenance on the system.

   • Some examples of commands found in this directory include fsck, init, shutdown, reboot, fdisk, ifconfig.

10. /bin :

    • The command binaries required for system operation, including those needed in single-user mode, are stored in this directory.

    • Many common Linux commands, such as cat, ls, and cp are stored here. These commands are frequently used for various system tasks and operations.

    • Commands located in /bin are accessible to all users of the system. Examples include ps, ping, grep, and cp , which are used by all users for different purposes.

11. /var :

    • The system uses changing data files stored in this directory while it operates.

    • It is the location where the system stores logs, temporary data, and other items that are subject to frequent changes while the system is operating.

    • Files such as system logs, pending emails, and temporary files can be found inside /var.

    • Users and system applications save and retrieve data via /var. Maintaining this directory correctly is essential to the system's functionality.

12. /mnt :

    • Users can temporarily mount network sites or external devices in this directory.

    • It acts as a point of connection between the system and devices such as network shares, USB drives, and external hard drives.

    • In order to access the contents of devices like USB drives or network folders, users frequently mount them to /mnt.

    • It serves as a temporary location for external data access. The files are removed from /mnt whenever the device or location is unmounted.

13. /media :

    • The system automatically mounts external devices, such as optical discs and USB drives, in this directory.

    • It's where, when you add in devices like USB drives or CDs, the system connects automatically and displays content from those sources.

    • The files on a USB drive or CD will appear under /media so you can quickly access them when you plug them in.

    • It serves as a space for short-term external device storage. The files vanish from /media as soon as the device is removed.

14. /tmp :

    • Temporary files that are required while programs are running are kept in this directory.

    • It functions similarly to a short-term storage space where programs can store files they require temporarily.

    • Programs may utilize the /tmp directory to hold temporary files while they are operating, such as while processing data or downloading files.

    • To prevent permanently filling up your storage, files in /tmp are typically automatically erased when your computer restarts or after a predetermined period of time.

Conclusion

• Files are easily found and managed in Linux thanks to its clean file organization into directories.

• Various directories perform different functions, such as storing temporary files (/tmp), storing changing data (/var), or containing critical programs (/bin).

• Users can add their own stuff in places like /usr/local or connect external devices in /mnt and /media, making Linux work just how they want.

• directories like /home give everyone their own space to keep their files safe, while /boot has what's needed to start up the system smoothly.

• It's crucial to take care of folders like /var and /tmp to keep the system stable and secure, as they handle important data and temporary files. Regular cleanup and following good practices help keep Linux running well.