Linux-Debian (Kali) Command Cheatsheet¶

Overview¶

Linux-Debian (Kali) Fundamentals

Kali Linux is a Debian-derived distribution designed for digital forensics and penetration testing:

APT Package Management: Debian's Advanced Package Tool
Bash Environment: Customizable shell and path configuration
File Permissions: Unix-style permission system (read/write/execute)
Process Management: Tools for monitoring and controlling system processes
Networking: Comprehensive network analysis and manipulation tools

[SP] System & Package Management¶

[APT] Package Management¶

APT Package Management

Command	Description	Common Use
`apt update`	Refresh package lists	`sudo apt update`
`apt upgrade`	Upgrade installed packages	`sudo apt upgrade`
`apt install`	Install new packages	`sudo apt install nmap`
`apt remove`	Remove packages	`sudo apt remove package`
`apt search`	Search for packages	`apt search "security scanner"`

Basic Operations¶

Essential APT Commands

# Update package database
sudo apt update

# Upgrade all installed packages
sudo apt upgrade

# Full upgrade (may remove packages)
sudo apt full-upgrade

# Install specific package
sudo apt install nmap wireshark metasploit-framework

# Remove package (keep config files)
sudo apt remove package-name

# Remove package and config files
sudo apt purge package-name

# Search for packages
apt search "penetration testing"

# Show package information
apt show nmap

# List installed packages
apt list --installed

# Clean up package cache
sudo apt autoremove
sudo apt autoclean

Common Issues

Use sudo for system-wide operations
apt update before apt upgrade
full-upgrade may remove conflicting packages
Check dependencies with apt-cache depends

Advanced Package Operations¶

Advanced APT Usage

# Download package without installing
apt download package-name

# Install specific version
sudo apt install package-name=version

# Hold package at current version
sudo apt-mark hold package-name

# Show changelog
apt changelog package-name

# Check for broken dependencies
sudo apt --fix-broken install

# Show package statistics
apt stats

[DPKG] Low-Level Package Management¶

DPKG - Direct Package Management

# Install local .deb package
sudo dpkg -i package.deb

# Remove package
sudo dpkg -r package-name

# List installed packages
dpkg -l

# Show package contents
dpkg -L package-name

# Find which package owns a file
dpkg -S /usr/bin/nmap

# Reconfigure package
sudo dpkg-reconfigure package-name

# Fix broken packages
sudo dpkg --configure -a

[FM] File Management¶

[PERM] File Permissions¶

Understanding Linux Permissions

Linux uses a 3-tier permission system:

User (u): File owner permissions
Group (g): Group member permissions
Others (o): Everyone else permissions

Permission Types: - Read (r): 4 - View file contents - Write (w): 2 - Modify file contents - Execute (x): 1 - Run as program

Permission Management¶

chmod - Change File Permissions

# Symbolic notation
chmod u+x script.sh          # Add execute for owner
chmod g-w file.txt           # Remove write for group
chmod o=r file.txt           # Set others to read-only
chmod a+w file.txt           # Add write for all (a=all)

# Octal notation (most common)
chmod 755 script.sh          # rwxr-xr-x (owner:rwx, group:r-x, others:r-x)
chmod 644 file.txt           # rw-r--r-- (owner:rw-, group:r--, others:r--)
chmod 600 secret.txt         # rw------- (owner:rw-, no access for others)

# Recursive directory permissions
chmod -R 755 directory/      # Apply to directory and contents
chmod -R u+w directory/      # Add write for owner recursively

# Common permission patterns:
# 755 - Executables, scripts
# 644 - Regular files, documents  
# 600 - Private files, keys
# 777 - Full access (dangerous!)

chown - Change File Ownership

# Change owner
sudo chown username file.txt

# Change owner and group
sudo chown username:group file.txt

# Change group only
sudo chgrp groupname file.txt

# Recursive ownership change
sudo chown -R username:group directory/

# Common usage patterns:
sudo chown www-data:www-data /var/www/html
sudo chown kali:kali ~/tools

Special Permissions¶

Advanced Permission Flags

# SetUID - Run as file owner
chmod u+s /usr/bin/passwd    # Always runs as root

# SetGID - Run as file group  
chmod g+s /usr/bin/write     # Runs as tty group

# Sticky Bit - Directory protection
chmod +t /tmp                # Only owner can delete files in /tmp

# Combined examples:
chmod 4755 script.sh         # SetUID with standard permissions
chmod 2755 directory/        # SetGID on directory
chmod 1777 /tmp              # Sticky bit on world-writable directory

[OPS] File Operations¶

Essential File Operations

# Copy files and directories
cp file1.txt file2.txt
cp -r dir1/ dir2/            # Recursive copy
cp -a source/ destination/    # Archive mode (preserve everything)

# Move/rename files
mv oldname.txt newname.txt
mv file.txt /path/to/destination/

# Remove files and directories
rm file.txt
rm -r directory/             # Recursive remove
rm -f file.txt               # Force remove (no prompt)

# Create directories
mkdir newdir
mkdir -p path/to/nested/dir  # Create parent directories

# View file contents
cat file.txt                 # Display entire file
less file.txt                # Page through file
head -n 10 file.txt          # First 10 lines
tail -n 10 file.txt          # Last 10 lines
tail -f logfile.txt          # Follow (live view)

File Finding & Analysis¶

Finding Files

# find command - most powerful
find /home -name "*.txt"                    # Find by name
find /var/log -type f -name "*.log"         # Only files
find / -type d -name "config" 2>/dev/null   # Only directories
find . -size +1M                            # Files larger than 1MB
find /etc -mtime -7                         # Modified in last 7 days

# locate - faster but depends on database
sudo updatedb                              # Update file database
locate "*.conf"
locate passwd

# which - find executables in PATH
which nmap
which python3

# whereis - find binaries, sources, manuals
whereis ls
whereis -b nmap                            # Only binaries

[USR] User & Environment¶

[ENV] Environment Variables¶

Understanding Environment Variables

Environment variables control shell behavior and store system information:

PATH: Directories searched for executables
HOME: User's home directory
USER: Current username
SHELL: Current shell program
PWD: Present working directory

Environment Management¶

Viewing and Setting Environment Variables

# View all environment variables
env
printenv

# View specific variable
echo $PATH
echo $HOME
printenv USER

# Set temporary variable (current session only)
export MY_VAR="value"
export PATH=$PATH:/new/directory

# Set for single command only
MY_VAR="value" command_name

# Remove variable
unset MY_VAR

# Common PATH modifications:
export PATH=$PATH:/usr/local/bin
export PATH=$HOME/tools:$PATH              # Prepend to PATH

Adding to PATH¶

Permanently Adding to PATH

# Temporary addition (current terminal only)
export PATH=$PATH:/home/kali/my_tools

# Permanent addition - edit ~/.bashrc
nano ~/.bashrc
# Add line:
export PATH=$PATH:/home/kali/my_tools

# Reload bash configuration
source ~/.bashrc
# or
. ~/.bashrc

# Verify PATH
echo $PATH | tr ':' '\n'

# Check if command is in PATH
which new_command

[BASHRC] Bash Configuration¶

Bash Configuration File

# Edit bash configuration
nano ~/.bashrc
nano ~/.bash_profile        # For login shells

# Common .bashrc additions:

# Aliases for frequently used commands
alias ll='ls -la'
alias ..='cd ..'
alias grep='grep --color=auto'
alias ports='netstat -tulpn'

# Custom prompt
PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

# Environment variables
export EDITOR=nano
export HISTSIZE=10000
export HISTFILESIZE=20000

# Function definitions
function mkcd() {
    mkdir -p "$1" && cd "$1"
}

# Source other files
if [ -f ~/.bash_aliases ]; then
    . ~/.bash_aliases
fi

Useful Bash Aliases for Kali

# Penetration testing aliases
alias scan='nmap -sC -sV -O'
alias quickscan='nmap -T4 -F'
alias vulnscan='nmap --script vuln'
alias webscan='gobuster dir -u'

# Network aliases
alias myip='curl ifconfig.me'
alias ports='netstat -tulpn'
alias listen='lsof -i -P -n | grep LISTEN'

# System monitoring
alias meminfo='free -m -l -t'
alias cpuinfo='lscpu'
alias diskusage='df -h'

# Git shortcuts
alias gs='git status'
alias gc='git commit'
alias gp='git push'

# Safety nets
alias rm='rm -i'              # Confirm before remove
alias cp='cp -i'              # Confirm before overwrite
alias mv='mv -i'              # Confirm before move

[NET] Networking¶

[SCAN] Network Scanning¶

Network Discovery Commands

# Show network interfaces
ip addr show
ip link show
ifconfig                    # Legacy, may not be installed

# Show routing table
ip route show
route -n

# Check connectivity
ping google.com
ping -c 4 8.8.8.8          # Send 4 packets

# Trace route
traceroute google.com
tracepath google.com

# DNS lookup
nslookup google.com
dig google.com
host google.com

# Network statistics
ss -tuln                    # Show listening ports
netstat -tuln               # Legacy equivalent
ss -tulpn                   # Show processes with ports

Advanced Network Tools¶

Kali-Specific Network Commands

# Nmap - network scanner
nmap 192.168.1.0/24                    # Network discovery
nmap -sS -sV -O target.com             # Stealth scan + version + OS
nmap -p 1-1000 target.com              # Port range scan
nmap --script vuln target.com          # Vulnerability scripts

# Netcat - network Swiss army knife
nc -zv target.com 1-1000               # Port scanning
nc -lvnp 4444                          # Listen for connection
nc target.com 80                       # Connect to service

# Tcpdump - packet analyzer
tcpdump -i eth0                        # Capture on interface
tcpdump host 192.168.1.100             # Capture specific host
tcpdump port 80                        # Capture HTTP traffic

# Wireshark/tshark
tshark -i eth0 -f "tcp port 80"        # Command-line packet capture

[CONN] Network Connections¶

File Transfer & Remote Access

# SCP - Secure copy
scp file.txt user@remote:/path/        # Copy to remote
scp user@remote:/path/file.txt .       # Copy from remote
scp -r directory/ user@remote:/path/   # Recursive copy

# SSH - Secure shell
ssh user@remote-server.com
ssh -p 2222 user@remote.com            # Custom port
ssh -i key.pem user@remote.com         # Key authentication

# wget - File download
wget https://example.com/file.zip
wget -O custom-name.zip https://example.com/file.zip
wget --user=username --password=pass https://example.com/file.zip

# curl - Data transfer
curl -O https://example.com/file.zip
curl -o custom-name.zip https://example.com/file.zip
curl -u username:password https://example.com/file.zip

# HTTP server (useful for file sharing)
python3 -m http.server 8000            # Python 3
python -m SimpleHTTPServer 8000        # Python 2

[PRC] Process Management¶

[PS] Process Control¶

Understanding Linux Processes

PID: Process ID (unique number)
PPID: Parent Process ID
UID: User ID of process owner
State: Running, sleeping, zombie, etc.

Process Monitoring Commands

# View running processes
ps aux                    # All processes detailed format
ps -ef                    # Full format listing
ps aux | grep "process-name"

# Interactive process viewers
top                       # Basic process monitor
htop                      # Enhanced top (install with: sudo apt install htop)

# Process tree
pstree                    # Visual process hierarchy
ps -ef --forest           # Process tree view

# Find process by port
lsof -i :80               # What's using port 80?
netstat -tulpn | grep :80 # Alternative method
ss -tulpn | grep :80      # Modern method

# Process information
cat /proc/PID/status      # Detailed process info

Process Control¶

Process Management Commands

# Kill processes
kill PID                  # Graceful termination (SIGTERM)
kill -9 PID               # Force kill (SIGKILL)
killall process-name      # Kill all processes by name
pkill -f "pattern"        # Kill by pattern match

# Process priority
nice -n 10 command        # Start with low priority
renice -n 5 PID           # Change running process priority

# Background and foreground
command &                 # Run command in background
jobs                      # List background jobs
fg %1                     # Bring job 1 to foreground
bg %1                     # Continue job 1 in background

# No hangup - keep process running after logout
nohup long-running-command &
disown                    # Remove from job table

[SEC] Security & Permissions¶

[SUDO] Privilege Escalation¶

Understanding sudo

sudo allows permitted users to execute commands as root or another user:

Configured in /etc/sudoers
Provides audit trail of privileged commands
More secure than shared root password

sudo Usage Examples

# Run single command as root
sudo apt update
sudo nano /etc/hosts

# Run command as specific user
sudo -u username command
sudo -u www-data whoami

# Switch to root shell
sudo -i                    # Login shell with root's environment
sudo -s                    # Shell with current environment
sudo su -                  # Switch to root

# Preserve environment variables
sudo -E command           # Keep user environment

# List allowed commands
sudo -l                   # What can current user run?

# Edit sudoers file safely
sudo visudo               # Always use visudo, never direct edit!

sudoers Configuration¶

Common sudoers Entries

# Sample /etc/sudoers entries:

# Allow user to run any command as root
username ALL=(ALL:ALL) ALL

# Allow user to run specific commands without password
username ALL=(ALL) NOPASSWD: /usr/bin/apt, /bin/systemctl

# Allow group members
%admin ALL=(ALL:ALL) ALL
%sudo ALL=(ALL:ALL) ALL

# Command aliases
Cmnd_Alias NETWORKING = /sbin/route, /sbin/ifconfig
user1 ALL=(ALL) NETWORKING

# Important: Always use visudo to edit!
sudo visudo

[PERM] Advanced Permissions¶

Advanced Permission Management

# View detailed file permissions
ls -la                    # Long listing with permissions
stat file.txt             # Detailed file information

# Access Control Lists (ACLs)
getfacl file.txt          # View ACLs
setfacl -m u:user:rw file.txt    # Add user ACL
setfacl -m g:group:rx file.txt   # Add group ACL
setfacl -x u:user file.txt       # Remove user ACL

# Default ACLs (inheritance)
setfacl -d -m u:user:rw directory/   # Default ACL for new files

# umask - default file permissions
umask                     # Show current umask
umask 022                 # Set umask (files: 644, dirs: 755)
umask 077                 # Restrictive (files: 600, dirs: 700)

[MISC] Miscellaneous¶

[ARCH] Archive & Compression¶

File Archiving Commands

# tar - tape archive
tar -czf archive.tar.gz directory/     # Create compressed tar
tar -xzf archive.tar.gz               # Extract compressed tar
tar -tf archive.tar.gz                # List contents without extracting

# zip/unzip
zip -r archive.zip directory/         # Create zip archive
unzip archive.zip                     # Extract zip
unzip -l archive.zip                  # List zip contents

# gzip/gunzip
gzip file.txt                         # Compress to file.txt.gz
gunzip file.txt.gz                    # Decompress

# 7zip (if installed)
7z a archive.7z directory/            # Create 7z archive
7z x archive.7z                       # Extract 7z

# Common compression options:
# -c: create, -x: extract, -z: gzip, -j: bzip2, -v: verbose, -f: file

[HIST] History & Search¶

Command History Management

# Command history
history                    # Show command history
!55                       # Execute command #55 from history
!!                        # Repeat last command
!nmap                     # Execute last nmap command

# Search history
Ctrl + R                  # Reverse search through history
history | grep "ssh"      # Search for commands containing "ssh"

# History configuration (~/.bashrc)
export HISTSIZE=10000     # Number of commands in memory
export HISTFILESIZE=20000 # Number of commands in history file
export HISTTIMEFORMAT="%d/%m/%y %T "  # Add timestamps
export HISTCONTROL=ignoredups:ignorespace  # Don't save duplicates

# Clear history
history -c                # Clear current session history
history -w                # Write current history to file

Directory Operations

# Basic navigation
pwd                       # Print working directory
cd /path/to/directory     # Change directory
cd ~                      # Home directory
cd -                      # Previous directory

# Directory stack
pushd /path/to/dir        # Save current dir, change to new
popd                      # Return to saved directory
dirs                      # Show directory stack

# Listing files
ls                        # Basic list
ls -la                    # Long list, all files (including hidden)
ls -lh                    # Human readable sizes
ls -ltr                   # Sort by time (reverse)
ls -d */                  # List only directories

# Create directory structure
mkdir -p project/{src,doc,test}   # Create multiple directories
mkdir -p path/to/nested/directory

Quick Reference Matrix¶

Linux Command Quick Reference

Task	Command	Example
Install Package	`apt install`	`sudo apt install nmap`
Update System	`apt update && apt upgrade`	`sudo apt update && sudo apt upgrade`
File Permissions	`chmod`	`chmod 755 script.sh`
File Ownership	`chown`	`sudo chown user:group file.txt`
Add to PATH	`export PATH=`	`export PATH=$PATH:/new/path`
Find Files	`find`	`find /home -name "*.txt"`
Process Info	`ps aux`	`ps aux \\| grep ssh`
Kill Process	`kill`	`kill -9 1234`
Network Scan	`nmap`	`nmap -sV target.com`
File Transfer	`scp`	`scp file.txt user@host:/path/`
Archive	`tar`	`tar -czf backup.tar.gz directory/`

OPSEC Considerations¶

Security Best Practices

File Permissions:

Avoid chmod 777 - use more restrictive permissions
Set proper ownership for sensitive files
Use umask 077 for private directories

System Security:

Regular updates: sudo apt update && sudo apt upgrade
Use sudo instead of su for accountability
Secure SSH configuration (/etc/ssh/sshd_config)
Firewall configuration with ufw or iptables

Privacy:

Clear command history when needed: history -c && history -w
Use encrypted directories for sensitive work
Secure file deletion: shred -u file.txt

Tool Installation¶

Essential Kali Tools¶

Installing Common Penetration Testing Tools

# Metasploit Framework
sudo apt install metasploit-framework

# Nmap - network scanner
sudo apt install nmap

# Wireshark - packet analyzer
sudo apt install wireshark

# Burp Suite - web proxy
sudo apt install burpsuite

# John the Ripper - password cracker
sudo apt install john

# Hydra - login cracker
sudo apt install hydra

# SQLMap - SQL injection tool
sudo apt install sqlmap

# Gobuster - directory brute forcer
sudo apt install gobuster

# Install all common tools
sudo apt install kali-linux-headless

Custom Tool Installation¶

Manual Tool Installation

# Clone from GitHub
git clone https://github.com/tool-author/tool-name.git
cd tool-name

# Python tools
pip3 install -r requirements.txt
python3 setup.py install

# Build from source
./configure
make
sudo make install

# Install .deb packages
wget https://example.com/tool.deb
sudo dpkg -i tool.deb
sudo apt --fix-broken install  # Fix dependencies if needed

Troubleshooting Common Issues¶

Common Problems and Solutions

# "Command not found" error
which command-name          # Check if command exists
echo $PATH                 # Check PATH variable

# Permission denied
ls -la file.txt            # Check permissions
sudo command               # Run as root if appropriate

# Package broken dependencies
sudo apt --fix-broken install
sudo dpkg --configure -a

# Service won't start
sudo systemctl status service-name
journalctl -u service-name

# Disk space issues
df -h                      # Check disk usage
du -sh directory/          # Check directory size

# Network connectivity
ping 8.8.8.8              # Check basic connectivity
ip route show             # Check routing table