Linux File System Hierarchy: Complete Guide

Table of Contents

Introduction

The Linux file system hierarchy is a standardized directory structure that organizes files and directories in a logical, hierarchical manner. Unlike Windows systems that use drive letters (C:, D:, etc.), Linux uses a single root directory (/) from which all other directories branch out like an inverted tree structure.

Understanding the file system hierarchy is crucial for: - System administration - Software development - Troubleshooting - Security management - Efficient system navigation

File System Hierarchy Standard (FHS)

The Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Linux distributions. It ensures consistency across different Linux distributions and provides guidelines for where specific types of files should be stored.

FHS Compliance Levels

| Level | Description | Examples | |-------|-------------|----------| | Required | Must be present | /bin, /etc, /lib, /root, /tmp | | Optional | May be present | /home, /mnt, /opt, /srv | | Deprecated | Should be avoided | /usr/tmp (use /tmp instead) |

Root Directory Structure

The root directory (/) is the top-level directory in the Linux file system hierarchy. All other directories are subdirectories of the root directory.

` / ├── bin/ # Essential user binaries ├── boot/ # Boot loader files ├── dev/ # Device files ├── etc/ # System configuration files ├── home/ # User home directories ├── lib/ # Essential shared libraries ├── lib64/ # 64-bit shared libraries ├── media/ # Removable media mount points ├── mnt/ # Temporary mount points ├── opt/ # Optional software packages ├── proc/ # Process and kernel information ├── root/ # Root user home directory ├── run/ # Runtime data ├── sbin/ # System binaries ├── srv/ # Service data ├── sys/ # System information ├── tmp/ # Temporary files ├── usr/ # User programs and data └── var/ # Variable data files `

Detailed Directory Descriptions

/bin (Essential User Binaries)

Contains essential command binaries that need to be available in single-user mode and for all users.

Common files: - ls - List directory contents - cp - Copy files - mv - Move/rename files - rm - Remove files - cat - Display file contents - bash - Bash shell - grep - Text search utility

Command to explore: `bash ls -la /bin file /bin/ls which ls `

Notes: - These binaries are essential for system recovery - Available even when /usr is not mounted - Symlinked to /usr/bin in many modern distributions

/boot (Boot Loader Files)

Contains files needed for the boot process, including the kernel and initial RAM disk.

Typical contents:

| File/Directory | Description | |----------------|-------------| | vmlinuz-* | Compressed Linux kernel | | initrd.img-* | Initial RAM disk | | grub/ | GRUB bootloader configuration | | config-* | Kernel configuration | | System.map-* | Kernel symbol table |

Commands to explore: `bash ls -la /boot du -h /boot cat /boot/grub/grub.cfg `

Notes: - Often mounted as separate partition - Critical for system boot process - Requires careful handling during updates

/dev (Device Files)

Contains device files that represent hardware devices and virtual devices.

Device file types:

| Type | Description | Example | |------|-------------|---------| | Block devices | Storage devices | /dev/sda1, /dev/nvme0n1 | | Character devices | Serial devices | /dev/tty1, /dev/random | | Symbolic links | Device aliases | /dev/cdrom → /dev/sr0 |

Common device files: `bash

Storage devices

Terminal devices

Special devices

Exploration commands: `bash ls -la /dev lsblk cat /proc/devices mknod /tmp/mydevice c 1 3 # Create character device `

/etc (Configuration Files)

Contains system-wide configuration files and shell scripts used during boot.

Important subdirectories and files:

| Path | Purpose | |------|---------| | /etc/passwd | User account information | | /etc/shadow | Encrypted passwords | | /etc/group | Group information | | /etc/fstab | File system table | | /etc/hosts | Static hostname resolution | | /etc/resolv.conf | DNS resolver configuration | | /etc/crontab | System-wide cron jobs | | /etc/init.d/ | System service scripts | | /etc/systemd/ | Systemd configuration | | /etc/ssh/ | SSH configuration |

Example configurations: `bash

View system information

Network configuration

User management

/home (User Home Directories)

Contains personal directories for regular users.

Structure: ` /home/ ├── user1/ │ ├── .bashrc │ ├── .profile │ ├── Documents/ │ ├── Downloads/ │ └── Desktop/ └── user2/ ├── .bashrc └── projects/ `

Commands: `bash

Navigate to home directory

List user home directories

Check disk usage

/lib and /lib64 (Essential Shared Libraries)

Contains shared library files needed by binaries in /bin and /sbin.

Library types:

| Extension | Type | Purpose | |-----------|------|---------| | .so | Shared object | Dynamic libraries | | .a | Archive | Static libraries | | .ko | Kernel object | Kernel modules |

Commands: `bash

List libraries

Check library dependencies

Find library files

/media and /mnt (Mount Points)

/media: Automatic mount points for removable media /mnt: Manual mount points for temporary file systems

Usage examples: `bash

Media mounts (automatic)

Manual mounts

Check mounted file systems

/opt (Optional Software)

Contains add-on software packages that are not part of the default installation.

Typical structure: ` /opt/ ├── google/ │ └── chrome/ ├── teamviewer/ └── custom-software/ ├── bin/ ├── lib/ └── etc/ `

/proc (Process Information)

Virtual file system that provides information about running processes and kernel parameters.

Important files and directories:

| Path | Information | |------|-------------| | /proc/cpuinfo | CPU information | | /proc/meminfo | Memory information | | /proc/version | Kernel version | | /proc/uptime | System uptime | | /proc/loadavg | System load average | | /proc/[PID]/ | Process-specific information |

Examples: `bash

System information

Process information

/root (Root User Home)

Home directory for the root user (system administrator).

Characteristics: - Located at /root, not /home/root - Contains root's personal files and configurations - Accessible only by root user

`bash

Switch to root (if permitted)

View root's environment

/run (Runtime Data)

Contains runtime data for processes started since last boot.

Contents: - Process ID files - Socket files - Temporary runtime data

`bash ls /run ls /run/user/$UID # User runtime directory `

/sbin (System Binaries)

Contains essential system administration binaries.

Common utilities: - fdisk - Disk partitioning - fsck - File system check - iptables - Firewall configuration - mount/umount - Mount file systems - ifconfig - Network interface configuration

`bash ls /sbin which fdisk /sbin/fdisk -l # List disk partitions `

/srv (Service Data)

Contains data for services provided by the system.

Examples: ` /srv/ ├── www/ # Web server data ├── ftp/ # FTP server data └── git/ # Git repositories `

/sys (System Information)

Virtual file system providing information about devices, drivers, and kernel features.

`bash

Hardware information

/tmp (Temporary Files)

Directory for temporary files that may be deleted between reboots.

Characteristics: - World-writable with sticky bit - Often mounted as tmpfs (RAM-based) - Files may be automatically cleaned

`bash ls -ld /tmp df /tmp

Create temporary file

/usr (User Programs)

Contains user programs and supporting files.

Subdirectories:

| Directory | Purpose | |-----------|---------| | /usr/bin | User binaries | | /usr/sbin | System administration binaries | | /usr/lib | Libraries for /usr/bin and /usr/sbin | | /usr/share | Shared data (documentation, icons) | | /usr/local | Locally installed software | | /usr/src | Source code | | /usr/include | Header files |

/var (Variable Data)

Contains files that change frequently during system operation.

Important subdirectories:

| Directory | Purpose | |-----------|---------| | /var/log | Log files | | /var/cache | Application cache | | /var/spool | Spool directories (mail, print) | | /var/tmp | Temporary files preserved between reboots | | /var/lib | Variable state information | | /var/run | Runtime variable data (often symlinked to /run) |

File Types in Linux

Linux recognizes several file types, each indicated by the first character in the long listing format.

| Symbol | Type | Description | Example | |--------|------|-------------|---------| | - | Regular file | Normal files | ls -l file.txt | | d | Directory | Folders | drwxr-xr-x 2 user group | | l | Symbolic link | Links to other files | lrwxrwxrwx 1 root root | | c | Character device | Serial devices | crw-rw-rw- 1 root tty | | b | Block device | Block devices | brw-rw---- 1 root disk | | p | Named pipe | FIFO pipes | prw-r--r-- 1 user group | | s | Socket | Unix sockets | srwxrwxrwx 1 user group |

Commands to identify file types: `bash file /bin/ls file /dev/sda1 file /etc/passwd ls -la | head -10 `

Navigation Commands

Basic Navigation

| Command | Purpose | Example | |---------|---------|---------| | pwd | Print working directory | pwd | | cd | Change directory | cd /etc | | ls | List directory contents | ls -la | | tree | Display directory tree | tree /etc |

Advanced Navigation

`bash

Change to previous directory

Go to parent directory

Go to home directory

Go to root directory

Navigate using absolute paths

Navigate using relative paths

Directory Listing Options

`bash

Long format with details

Include hidden files

Human-readable sizes

Sort by modification time

Recursive listing

List directories only

List with inode numbers

File System Operations

Creating Files and Directories

`bash

Create empty file

Create multiple files

Create directory

Create nested directories

Create directory with specific permissions

Copying and Moving

`bash

Copy file

Copy directory recursively

Copy preserving attributes

Move/rename file

Move to different directory

Removing Files and Directories

`bash

Remove file

Remove multiple files

Remove directory and contents

Force removal without prompts

Interactive removal

Remove empty directory

Finding Files

`bash

Find by name

Find by type

Find by size

Find by permissions

Find and execute command

Locate command (faster, uses database)

Permissions and Ownership

Understanding Permissions

Linux uses a three-tiered permission system: - User (u): File owner - Group (g): Group members - Other (o): Everyone else

Permission types: - Read (r): View file contents or list directory - Write (w): Modify file or directory contents - Execute (x): Run file or access directory

Permission Representation

| Octal | Binary | Symbolic | Permissions | |-------|--------|----------|-------------| | 0 | 000 | --- | No permissions | | 1 | 001 | --x | Execute only | | 2 | 010 | -w- | Write only | | 3 | 011 | -wx | Write and execute | | 4 | 100 | r-- | Read only | | 5 | 101 | r-x | Read and execute | | 6 | 110 | rw- | Read and write | | 7 | 111 | rwx | All permissions |

Changing Permissions

`bash

Using octal notation

Using symbolic notation

Recursive permission change

Changing Ownership

`bash

Change owner

Change owner and group

Change group only

Recursive ownership change

Special Permissions

| Permission | Octal | Effect | |------------|-------|--------| | Sticky bit | 1000 | Only owner can delete files in directory | | SGID | 2000 | Execute with group privileges | | SUID | 4000 | Execute with owner privileges |

`bash

Set sticky bit (commonly on /tmp)

Set SUID bit

Set SGID bit

Mount Points and File Systems

Understanding Mount Points

A mount point is a directory where a file system is attached to the directory tree.

Viewing Mounted File Systems

`bash

Show all mounted file systems

Show in human-readable format

Show specific file system type

Show mount options

Manual Mounting

`bash

Create mount point

Mount device

Mount with specific options

Unmount

Permanent Mounts (/etc/fstab)

The /etc/fstab file defines file systems to be mounted at boot.

Format: ` device mountpoint filesystem options dump pass `

Example: `bash

/etc/fstab

File System Types

| Type | Description | Use Case | |------|-------------|----------| | ext4 | Fourth extended file system | Linux default | | xfs | High-performance file system | Large files, RHEL default | | btrfs | B-tree file system | Advanced features, snapshots | | ntfs | Windows NT file system | Windows compatibility | | vfat | Virtual FAT | USB drives, compatibility | | tmpfs | Temporary file system | RAM-based storage |

Best Practices

File System Navigation

File Management

Security Considerations

System Maintenance

Command Safety

Always verify before destructive operations

Use safe copying

Test commands safely

This comprehensive guide provides a thorough understanding of the Linux file system hierarchy, essential for anyone working with Linux systems. The hierarchical structure, while initially complex, follows logical patterns that become intuitive with practice and regular use.