Filesystem Hierarchy Standard (FHS)

The Filesystem Hierarchy Standard (FHS) is a reference describing the conventions used for the layout of a UNIX system. It has been made popular by its use in Linux distributions, but it is used by other UNIX variants as well.

Purpose

The FHS was created to provide a standardized directory structure for UNIX-like operating systems. This standardization helps users and developers predict where to find files and directories, making it easier to:

• Write and maintain software that works across different UNIX systems
• Understand where to find system files and programs
• Maintain consistency across different Linux distributions

Key Directories

• /bin - Essential command binaries that all users may need
• /boot - Static files of the boot loader
• /dev - Device files
• /etc - Host-specific system configuration
• /home - User home directories
• /lib - Essential shared libraries and kernel modules
• /mnt - Mount point for temporarily mounted filesystems
• /opt - Optional application software packages
• /proc - Virtual filesystem providing process and kernel information
• /root - Home directory for the root user
• /sbin - Essential system binaries
• /tmp - Temporary files
• /usr - Secondary hierarchy for read-only user data
• /var - Variable files

Benefits

Following the FHS provides several advantages:

• Predictable system layout across different distributions
• Easier software installation and maintenance
• Better system administration and troubleshooting
• Improved compatibility between different UNIX-like systems

Version History

The FHS has evolved over time, with major versions including:

• FHS 1.0 (1994)
• FHS 2.0 (1997)
• FHS 2.1 (2000)
• FHS 2.2 (2001)
• FHS 2.3 (2004)
• FHS 3.0 (2015)

The standard is maintained by the Linux Foundation and continues to be updated to reflect modern UNIX and Linux system needs.