LWM-Linux/01 - Introduction to Linux/Linux Filesystem Hierarchy Standard (LFHS).md

Linux Filesystem Hierarchy Standard (LFHS)

The Linux Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Linux and other Unix-like operating systems. It is maintained by the Linux Foundation and provides consistency across distributions. Let's explore the main directories and their purposes:

1. / (Root Directory)

The root directory is the top-level directory of the filesystem. All other directories are subdirectories of the root.

2. /bin (Essential User Binaries)

Contains essential command binaries that need to be available in single-user mode. Examples include ls, cp, and pwd.

3. /boot (Boot Loader Files)

Contains files needed for the boot process, including the kernel, initrd, and boot loader configuration.

4. /dev (Device Files)

Contains device files, which are interfaces for device drivers. Examples include /dev/sda for the first SATA drive and /dev/tty for terminals.

5. /etc (Configuration Files)

Stores system-wide configuration files and scripts. Examples include /etc/passwd for user information and /etc/fstab for filesystem information.

6. /home (User Home Directories)

Contains home directories for regular users. Each user typically has a subdirectory here, like /home/username.

7. /lib (Essential Shared Libraries)

Holds library files needed by the binaries in /bin and /sbin.

8. /media (Removable Media)

Mount point for removable media such as USB drives and CD-ROMs.

9. /mnt (Temporary Mount Points)

Used for temporarily mounted filesystems.

10. /opt (Optional Software)

Reserved for the installation of add-on application software packages.

11. /proc (Process Information)

A virtual filesystem providing process and kernel information as files.

12. /root (Root User Home Directory)

Home directory for the root user.

13. /run (Run-time Variable Data)

Contains variable data files describing the system since the last boot.

14. /sbin (System Binaries)

Similar to /bin, but contains binaries essential for system administration, usually to be run by root.

15. /srv (Service Data)

Contains data for services provided by the system.

16. /sys (System Information)

A virtual filesystem providing a standardized interface to kernel objects.

17. /tmp (Temporary Files)

Directory for temporary files. Often cleared on reboot.

18. /usr (User Programs)

Contains the majority of user utilities and applications. It has several subdirectories:

• /usr/bin: Non-essential command binaries
• /usr/lib: Libraries for /usr/bin and /usr/sbin
• /usr/local: Local hierarchy for system administrators
• /usr/sbin: Non-essential system binaries
• /usr/share: Architecture-independent data

19. /var (Variable Files)

Contains variable data files, including logs (/var/log), temporary email files (/var/mail), and spooled files (/var/spool).

20. Key Principles of FHS:

• 1. Separation of core system files from user files
• 2. Consistency across distributions
• 3. Backward compatibility
• 4. Flexibility for system administrators

21. Benefits of FHS:

• 1. Easier system administration
• 2. Improved security through proper file organization
• 3. Compatibility across different Linux distributions
• 4. Easier software development and deployment

LFHS