RED HAT ENTERPRISE LINUX

Navigating the
Filesystem Hierarchy

Understanding the Linux Directory Structure

CIS126RH | RHEL System Administration 1
Mesa Community College

Learning Objectives

Understand the FHS structure

Learn the purpose of major directories in the hierarchy

Navigate with paths

Use absolute and relative paths effectively

Master navigation commands

Use pwd, cd, ls, and tree to explore the filesystem

Locate important system files

Know where to find configs, logs, binaries, and data

The Filesystem Hierarchy Standard

The Filesystem Hierarchy Standard (FHS) defines the directory structure and contents in Unix-like operating systems. It provides predictability — administrators know where to find files regardless of which Linux distribution they use.

Key Principles

Single root (/) hierarchy
Everything is a file
Separation of static vs variable data
Separation of shareable vs local data

Benefits

Consistent across distributions
Easier system administration
Simplified software packaging
Clear organization of data

The Root Directory

/ ← Root of the entire filesystem
├── bin/ Essential user binaries
├── boot/ Boot loader files, kernel
├── dev/ Device files
├── etc/ System configuration
├── home/ User home directories
├── root/ Root user's home
├── tmp/ Temporary files
├── usr/ User programs and data
└── var/ Variable data (logs, spool)

Note: The root directory (/) is different from the root user's home directory (/root).

Essential Directories Part 1

Directory	Purpose	Examples
/bin	Essential user commands	ls, cp, mv, cat, bash
/sbin	Essential system binaries	fdisk, fsck, init, ip
/boot	Boot loader and kernel	vmlinuz, initramfs, grub2
/dev	Device files	sda, tty, null, random
/etc	System configuration	passwd, fstab, ssh/sshd_config
/lib, /lib64	Essential shared libraries	libc.so, ld-linux.so

RHEL 9 Note: /bin, /sbin, /lib, /lib64 are now symlinks to their equivalents under /usr (the "usr merge").

Essential Directories Part 2

Directory	Purpose	Examples
/home	User home directories	/home/student, /home/admin
/root	Root user's home directory	.bashrc, .ssh/
/tmp	Temporary files (cleared on boot)	Session data, downloads
/var	Variable data	logs, mail, databases
/proc	Process and kernel information (virtual)	cpuinfo, meminfo, [pid]/
/sys	Device and kernel information (virtual)	block/, class/, devices/

⚠ Important: /proc and /sys are virtual filesystems — they don't exist on disk but provide real-time system information.

The /usr Directory

/usr (Unix System Resources) contains the majority of user applications, libraries, and documentation. It is often the largest directory on a system.

/usr/
├── bin/ User commands (merged with /bin)
├── sbin/ System admin commands (merged with /sbin)
├── lib/ Libraries for /usr/bin, /usr/sbin
├── lib64/ 64-bit libraries
├── local/ Locally installed software
├── share/ Architecture-independent data
│ ├── doc/ Documentation
│ └── man/ Manual pages
└── src/ Source code

The /var and /etc Directories

/var — Variable Data

/var/log

System and application log files

/var/lib

Application state data (databases, package info)

/var/spool

Queued data (print jobs, mail, cron)

/var/cache

Application cache data (dnf, man-db)

/etc — Configuration

/etc/passwd

User account information

/etc/fstab

Filesystem mount configuration

/etc/ssh/

SSH server and client configuration

/etc/systemd/

Systemd unit file overrides

Pro Tip: Always back up files before editing: cp file file.bak

Special Directories

/proc

Virtual filesystem. /proc/cpuinfo, /proc/meminfo, /proc/[pid]/ — queries kernel in real time

/sys

Virtual filesystem for device and driver information. Used for hardware configuration.

/run

Runtime data since boot. PID files, sockets, tmpfs mounted. Cleared on reboot.

/mnt

Temporary mount point for manual mounts. Convention for admin-mounted filesystems.

/media

Mount point for removable media. USB drives, DVDs auto-mount here.

/opt

Optional software packages. Third-party applications often install here.

Absolute vs Relative Paths

Absolute Path

Starts from root (/)
Complete path to file
Works from anywhere

/home/student/documents/report.txt

Relative Path

Starts from current directory
Shorter to type
Context-dependent

documents/report.txt

# Absolute path — starts with /
cat /etc/passwd
cd /var/log

# Relative path — from current directory
[student@server ~]$ cd documents
[student@server documents]$ cat report.txt

# Special relative references
.     # Current directory
..    # Parent directory
~     # Home directory

Path Examples

# Starting position: /home/student
[student@server ~]$ pwd
/home/student

# Relative navigation
[student@server ~]$ cd documents         # → /home/student/documents
[student@server documents]$ cd ..        # → /home/student
[student@server ~]$ cd ../admin          # → /home/admin
[student@server admin]$ cd ~             # → /home/student

# Absolute navigation
[student@server ~]$ cd /var/log          # → /var/log
[student@server log]$ cd /etc/ssh        # → /etc/ssh

# Return to previous directory
[student@server ssh]$ cd -               # → /var/log
/var/log

Navigation: pwd and cd

# pwd — Print Working Directory
pwd
/home/student

# cd — Change Directory
cd /var/log           # Go to absolute path
cd log                # Go to subdirectory (relative)
cd ..                 # Go to parent directory
cd ../..              # Go up two levels
cd                    # Go to home directory
cd ~                  # Go to home directory (explicit)
cd ~username          # Go to another user's home
cd -                  # Go to previous directory

Common mistake — spaces in paths:
cd /home/My Documents → ERROR (two arguments)
cd "/home/My Documents" → Correct (quoted)
cd /home/My\ Documents → Correct (escaped space)

Listing Files: ls

# Basic listing
ls                    # List current directory
ls /etc               # List specific directory

# Common options
ls -l                 # Long format (permissions, size, date)
ls -a                 # Show hidden files (starting with .)
ls -la                # Long format + hidden files
ls -lh                # Human-readable sizes (K, M, G)
ls -lt                # Sort by modification time
ls -ltr               # Sort by time, reversed (oldest first)
ls -R                 # Recursive listing
ls -d */              # List only directories

# Output example
ls -lh /etc/passwd
-rw-r--r--. 1 root root 2.3K Dec  1 10:30 /etc/passwd

Understanding ls -l Output


            -rw-r--r--. 1 root root 2.3K Dec  1 10:30 /etc/passwd

Field	Example	Meaning
File type + permissions	`-rw-r--r--`	Regular file; owner rw, others r
Link count	`1`	Number of hard links
Owner	`root`	User who owns the file
Group	`root`	Group that owns the file
Size	`2.3K`	File size (with -h flag)
Modified	`Dec 1 10:30`	Last modification date/time

Visualizing with tree

# Install tree if not present
sudo dnf install tree

# Basic tree view
tree /etc/ssh
/etc/ssh
├── moduli
├── ssh_config
├── ssh_config.d
│   └── 50-redhat.conf
├── sshd_config
└── sshd_config.d
    └── 50-redhat.conf

# Useful options
tree -L 2             # Limit depth to 2 levels
tree -d               # Directories only
tree -a               # Show hidden files
tree -h               # Show file sizes
tree -p               # Show permissions
tree --dirsfirst      # Directories before files

Finding Your Way

# Where am I?
pwd

# What's here?
ls -la

# Where is a command located?
which python
/usr/bin/python

whereis bash
bash: /usr/bin/bash /usr/share/man/man1/bash.1.gz

# Find a file (fast — uses database)
locate passwd

# Find a file (thorough — searches live filesystem)
find /etc -name "passwd"

# What type of content is this?
file /etc/passwd
/etc/passwd: ASCII text

Tab Completion

Tab completion automatically completes commands, paths, and filenames when you press the Tab key — saving time and preventing typos.

# Type partial path, press Tab to complete
cd /etc/sys[TAB]
cd /etc/sysconfig/           # Completed!

# Multiple matches? Press Tab twice to list
cd /etc/sys[TAB][TAB]
sysconfig/  sysctl.conf  sysctl.d/  systemd/

# Works with commands too
syste[TAB]
systemctl                    # Completed!

# And with options (with bash-completion)
systemctl st[TAB][TAB]
start   status  stop

Pro Tip: If Tab does not complete, the path does not exist. This catches typos immediately rather than when the command fails.

Key Takeaways

The FHS provides a consistent directory structure across Linux systems

Absolute paths start with /, relative paths start from the current directory

Key commands: pwd cd ls tree

Know where to find: /etc (config), /var/log (logs), /home (users), /usr (programs)

Graded Lab

Navigate to /var/log and list files sorted by modification time
Use tree to visualize the /etc/ssh directory structure
Find all files named "passwd" anywhere on the system
Practice using relative paths with .. and . to navigate
Explore /proc/cpuinfo and /proc/meminfo

Next: Managing Files from the Command Line