Linux Command Line Essentials for Security Professionals

# Change directory
cd /path/to/directory

# List files and directories
ls -la

# Print working directory
pwd

# Create directory
mkdir new_directory

# Remove file or directory
rm file.txt
rm -rf directory/

# View file contents
cat file.txt
less file.txt
head -n 20 file.txt
tail -f logfile.log

# Search within files
grep "pattern" file.txt
grep -r "pattern" /directory/

# Find files
find / -name "filename"
find / -type f -size +100M

# Copy and move
cp source.txt destination.txt
mv old_name.txt new_name.txt

# Change file permissions
chmod 755 script.sh
chmod +x executable

# Change file ownership
chown user:group file.txt

# View permissions
ls -l file.txt

# View running processes
ps aux
top
htop

# Kill a process
kill PID
kill -9 PID  # Force kill

# Run process in background
command &

# View background jobs
jobs

# Bring to foreground
fg %1

# Check network interfaces
ip addr
ifconfig

# Test connectivity
ping 8.8.8.8
ping -c 4 google.com

# DNS lookup
nslookup domain.com
dig domain.com

# Network connections
netstat -tuln
ss -tuln

# Download files
wget https://example.com/file.zip
curl -O https://example.com/file.zip

# Search and replace
sed 's/old/new/g' file.txt

# Pattern processing
awk '{print $1}' file.txt

# Sort and unique
sort file.txt
uniq file.txt
sort file.txt | uniq -c

# Count lines, words, characters
wc -l file.txt

# Pipe output to another command
cat file.txt | grep "error" | wc -l

# Redirect output to file
command > output.txt
command >> output.txt  # Append

# Redirect error output
command 2> error.log
command &> all_output.log

# Disk usage
df -h
du -sh /path/

# Memory usage
free -h

# System information
uname -a
cat /etc/os-release

# Uptime and load
uptime

# Check open ports
sudo netstat -tulpn
sudo ss -tulpn

# View system logs
sudo tail -f /var/log/syslog
sudo journalctl -f

# Check failed login attempts
sudo cat /var/log/auth.log | grep "Failed"

# View active network connections
sudo lsof -i

# Check for setuid binaries
find / -perm -4000 2>/dev/null

alias ll='ls -lah'
alias update='sudo apt update && sudo apt upgrade'
alias ports='sudo netstat -tulpn'