Bash: Getting Around Linux

The Linux command line is your most powerful tool as a penetration tester. Navigating the filesystem, understanding directory structure, and mastering basic commands is absolutely essential. This lesson covers the fundamental skills you need to move around Linux like a pro.

What You'll Learn

Linux filesystem structure
Essential navigation commands
Understanding paths (absolute vs relative)
Working with directories
Finding files and commands
Understanding your current context
Command shortcuts and efficiency tips

The Linux Filesystem Hierarchy

Everything Starts at Root:

/
└── Root directory (top of filesystem)

Linux uses forward slashes: /
Windows uses backslashes: \

Everything branches from /

Key Directories:

/
├── bin/        # Essential user binaries (ls, cat, cp)
├── sbin/       # System binaries (iptables, fdisk)
├── etc/        # Configuration files
├── home/       # User home directories
│   └── user/   # Your home directory
├── root/       # Root user's home directory
├── tmp/        # Temporary files (world-writable)
├── var/        # Variable data (logs, caches)
│   └── log/    # Log files
├── usr/        # User programs and data
│   ├── bin/    # User binaries
│   ├── local/  # Locally installed software
│   └── share/  # Shared data
├── opt/        # Optional/add-on software
├── proc/       # Process information (virtual)
├── sys/        # System information (virtual)
├── dev/        # Device files
└── mnt/        # Mount points for external filesystems

1. pwd - Print Working Directory

What it does: Shows your current location

pwd

Output:

/home/kali

Use case: Orient yourself when you're lost

2. ls - List Directory Contents

Basic usage:

ls

Shows files and directories in current location.

Common options:

# Long format (permissions, owner, size, date)
ls -l

# Show hidden files (starting with .)
ls -a

# Human-readable sizes
ls -lh

# Sort by modification time (newest first)
ls -lt

# Reverse order
ls -lr

# Combine options
ls -lah

Output examples:

$ ls -lah
total 48K
drwxr-xr-x  6 kali kali 4.0K Jan  1 12:00 .
drwxr-xr-x 20 root root 4.0K Jan  1 11:00 ..
-rw-r--r--  1 kali kali  220 Jan  1 10:00 .bashrc
drwxr-xr-x  2 kali kali 4.0K Jan  1 12:00 Documents
-rw-r--r--  1 kali kali 1.5K Jan  1 11:30 file.txt
drwxr-xr-x  2 kali kali 4.0K Jan  1 12:00 Downloads

Understanding the output:

drwxr-xr-x = Permissions
6          = Number of links
kali       = Owner
kali       = Group
4.0K       = Size
Jan 1      = Date
12:00      = Time
Documents  = Name

List specific directory:

ls /etc
ls /var/log
ls ~/Documents

3. cd - Change Directory

Basic usage:

cd /path/to/directory

Common shortcuts:

# Go to home directory
cd
cd ~

# Go to root directory
cd /

# Go up one level
cd ..

# Go up two levels
cd ../..

# Go to previous directory
cd -

# Go to specific user's home
cd ~username

Examples:

# Absolute path
cd /var/log

# Relative path (from current location)
cd Documents

# Multiple levels
cd ../../etc

# Back and forth
cd /tmp
cd -  # Returns to previous directory

4. tree - Display Directory Tree

Install (if not present):

sudo apt install tree

Usage:

# Show tree of current directory
tree

# Limit depth
tree -L 2

# Show hidden files
tree -a

# Only directories
tree -d

# Show file sizes
tree -h

Output:

.
├── Documents
│   ├── notes.txt
│   └── report.pdf
├── Downloads
│   └── tool.zip
└── scripts
    ├── recon.sh
    └── scan.py

3 directories, 5 files

Understanding Paths

Absolute Paths:

# Start with / (root)
/home/kali/Documents/file.txt
/etc/passwd
/var/log/syslog

Always works regardless of current directory

Relative Paths:

# Relative to current directory
Documents/file.txt
./script.sh
../other_directory/file.txt

Depends on where you are (pwd)

Special Path Symbols:

.   = Current directory
..  = Parent directory
~   = Home directory
-   = Previous directory
/   = Root directory

Examples:

# Current directory
./script.sh
ls .

# Parent directory
cd ..
ls ../

# Home directory
cd ~
ls ~/Documents

# Combining
cd ~/Documents/../../etc  # Works but confusing!

Finding Files and Directories

1. which - Locate a Command

# Find where a command is located
which python3
# Output: /usr/bin/python3

which nmap
# Output: /usr/bin/nmap

2. whereis - Locate Binary, Source, and Manual

whereis ls
# Output: ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz

3. locate - Quick File Search

# Fast search (uses database)
locate file.txt

# Case-insensitive
locate -i FILE.TXT

# Update database (run as root)
sudo updatedb

Note: locate is fast but may not show recently created files until you run updatedb.

4. find - Powerful File Search

# Find by name
find /path -name "filename"

# Case-insensitive
find /path -iname "filename"

# Find directories only
find /path -type d -name "dirname"

# Find files only
find /path -type f -name "filename"

# Find by extension
find /path -name "*.txt"

# Find by size
find /path -size +10M  # Larger than 10MB
find /path -size -1M   # Smaller than 1MB

# Find by modification time
find /path -mtime -7   # Modified in last 7 days
find /path -mtime +30  # Modified more than 30 days ago

# Find and execute
find /path -name "*.log" -delete
find /path -name "*.sh" -exec chmod +x {} \;

Examples:

# Find all Python scripts in current directory
find . -name "*.py"

# Find SUID binaries (privilege escalation!)
find / -perm -4000 -type f 2>/dev/null

# Find writable directories
find / -type d -writable 2>/dev/null

# Find files owned by specific user
find / -user root -name "*.conf" 2>/dev/null

Working with Directories

Create Directories:

# Create single directory
mkdir mydir

# Create multiple directories
mkdir dir1 dir2 dir3

# Create nested directories
mkdir -p parent/child/grandchild

# Create with specific permissions
mkdir -m 755 mydir

Remove Directories:

# Remove empty directory
rmdir dirname

# Remove directory and contents
rm -r dirname

# Force remove without confirmation
rm -rf dirname  # ⚠️ DANGEROUS! No undo!

Understanding Your Context

Who am I?

whoami
# Output: kali

What groups am I in?

groups
# Output: kali sudo netdev

Full user information:

id
# Output: uid=1000(kali) gid=1000(kali) groups=1000(kali),27(sudo)

What system am I on?

hostname
# Output: kali

# Full hostname
hostname -f
# Output: kali.localdomain

# IP address
hostname -I
# Output: 192.168.1.100

What's the OS?

uname -a
# Output: Linux kali 5.18.0-kali5-amd64 #1 SMP PREEMPT_DYNAMIC Debian 5.18.5-1kali6 (2022-07-07) x86_64 GNU/Linux

# Just the kernel version
uname -r
# Output: 5.18.0-kali5-amd64

# OS information
cat /etc/os-release

Command Shortcuts and Tips

Tab Completion:

# Type first few letters, press TAB
cd Doc<TAB>  # Completes to: cd Documents/

# TAB twice to see all options
cd D<TAB><TAB>  # Shows: Desktop/ Documents/ Downloads/

Command History:

# View command history
history

# Search history (Ctrl+R)
# Press Ctrl+R, type search term, press Enter

# Run previous command
!!

# Run command #123 from history
!123

# Run last command starting with "nmap"
!nmap

# Clear history
history -c

# Jump to beginning of line
Ctrl+A

# Jump to end of line
Ctrl+E

# Clear screen
Ctrl+L
# Or: clear

# Cancel current command
Ctrl+C

# Logout/exit shell
Ctrl+D
# Or: exit

Useful Aliases:

Add to ~/.bashrc:

alias ll='ls -lah'
alias la='ls -A'
alias l='ls -CF'
alias ..='cd ..'
alias ...='cd ../..'
alias grep='grep --color=auto'

After adding, reload:

source ~/.bashrc

Practical Exercises

Exercise 1: Navigate the Filesystem

# 1. Where am I?
pwd

# 2. What's here?
ls -la

# 3. Go to root
cd /

# 4. List root directories
ls

# 5. Go to /etc
cd /etc

# 6. Go back home
cd ~

# 7. Go to /var/log
cd /var/log

# 8. Go back to previous directory
cd -

Exercise 2: Find Files

# Find all .txt files in home directory
find ~ -name "*.txt"

# Find all Python scripts
find ~ -name "*.py"

# Find where 'nmap' is installed
which nmap

# Find all files modified today
find ~ -type f -mtime 0

Exercise 3: Explore Directories

# List contents of /etc with details
ls -lah /etc

# Show directory tree of home (2 levels)
tree -L 2 ~

# Find all directories in /var
find /var -type d 2>/dev/null | head -20

Exercise 4: Practice Paths

# Create test structure
mkdir -p ~/test/level1/level2/level3

# Navigate with relative paths
cd ~/test
cd level1
cd ../
cd level1/level2
cd ../../

# Navigate with absolute paths
cd /home/$USER/test/level1/level2/level3
pwd

Common Mistakes to Avoid

1. Not Using Tab Completion:

❌ Typing full paths manually
✅ Use TAB completion

2. Forgetting Where You Are:

# Always check before dangerous commands
pwd
ls

# Then execute
rm -rf dirname

3. Case Sensitivity:

# Linux is case-sensitive!
cd Documents  # ✅
cd documents  # ❌ (if directory is "Documents")

4. Spaces in Paths:

# Use quotes or escape spaces
cd "My Documents"
cd My\ Documents

# Or avoid spaces in filenames!
mkdir my-documents  # Better

5. Dangerous Commands:

# NEVER run without understanding!
rm -rf /    # Deletes EVERYTHING (requires --no-preserve-root)
rm -rf .    # Deletes current directory contents
rm -rf ~    # Deletes your home directory

# Always double-check:
ls dirname    # Confirm it's what you want
rm -rf dirname  # Then delete

Quick Reference

Navigation:
pwd              # Print working directory
ls               # List contents
ls -lah          # Detailed list with hidden files
cd /path         # Change directory
cd ~             # Go home
cd ..            # Go up one level
cd -             # Go to previous directory

Finding:
which cmd        # Find command location
whereis cmd      # Find binary/man page
locate file      # Fast search (uses database)
find / -name f   # Powerful search

Directories:
mkdir dir        # Create directory
mkdir -p a/b/c   # Create nested directories
rmdir dir        # Remove empty directory
rm -r dir        # Remove directory and contents

Context:
whoami           # Current user
hostname         # System name
pwd              # Current location
uname -a         # System information

Shortcuts:
TAB              # Auto-complete
Ctrl+R           # Search history
!!               # Run last command
Ctrl+C           # Cancel command
Ctrl+L           # Clear screen

Resources

Man Pages:

man ls
man cd
man find
man bash

Online Resources:

Linux Journey: https://linuxjourney.com
Explain Shell: https://explainshell.com
TLDR Pages: https://tldr.sh

Practice:

OverTheWire: Bandit: https://overthewire.org/wargames/bandit/
Local Linux VM (Kali, Ubuntu, etc.)

Next Steps

Master these basic commands through daily practice
Memorize the filesystem hierarchy (/etc, /var, /home, etc.)
Use tab completion religiously
Learn find deeply - it's incredibly powerful
Practice on OverTheWire Bandit levels 0-10

Navigation is the foundation of everything else. Master it before moving forward!

"Get lost in Linux so you can find your way around anywhere."

Bash: Getting Around Linux

What You'll Learn

The Linux Filesystem Hierarchy

Everything Starts at Root:

Key Directories:

Essential Navigation Commands

1. pwd - Print Working Directory

2. ls - List Directory Contents

3. cd - Change Directory

4. tree - Display Directory Tree

Understanding Paths

Absolute Paths:

Relative Paths:

Special Path Symbols:

Finding Files and Directories

1. which - Locate a Command

2. whereis - Locate Binary, Source, and Manual

3. locate - Quick File Search

4. find - Powerful File Search

Working with Directories

Create Directories:

Remove Directories:

Understanding Your Context

Who am I?

What groups am I in?

Full user information:

What system am I on?

What's the OS?

Command Shortcuts and Tips

Tab Completion:

Command History:

Quick Navigation:

Useful Aliases:

Practical Exercises

Exercise 1: Navigate the Filesystem

Exercise 2: Find Files

Exercise 3: Explore Directories

Exercise 4: Practice Paths

Common Mistakes to Avoid

1. Not Using Tab Completion:

2. Forgetting Where You Are:

3. Case Sensitivity:

4. Spaces in Paths:

5. Dangerous Commands:

Quick Reference

Resources

Man Pages:

Online Resources:

Practice:

Next Steps