Linux Syntax Cheat Sheet

# Using apt-get
sudo apt-get update
sudo apt-get install -y curl vim tree openssh-client openssh-server git nano mtr iptables ufw

# Using yum
sudo yum update
sudo yum install -y curl vim tree openssh-clients openssh-server git nano mtr iptables-services firewalld

# Create a directory and navigate into it
mkdir -p ~/script_demo/logs && cd ~/script_demo

# Initialize a new Git repository
git init
echo "Git repository initialized."

# Prepare Logs
touch logs/network_log.txt logs/process_log.txt logs/disk_log.txt logs/user_info.txt logs/system_info.txt

# Make any desired initial edits to logs files (to be done manually with nano or another text editor)
# nano logs/[desired_log_file].txt

# Stage and commit logs to the repository
git add logs/*.txt
git commit -m "Initial commit with logs"
echo "Logs committed to the repository."

#!/bin/bash

# Grab information about the current user and add it to a log
echo "Current user info:" > logs/user_info.txt
whoami >> logs/user_info.txt
echo "User info logged." # Expected action: User information written to log

# Add a test user and set a temporary password
echo "Adding test user..."
sudo useradd testuser
echo testuser:Temp1234 | sudo chpasswd
echo "Test user added and password set to a simple temporary one."
echo -e "\nTest User: testuser" >> logs/user_info.txt # Append test user info to logs/user_info.txt

# Create a new group named 'samplegroup'
sudo groupadd samplegroup

# Add the current user and 'testuser' to 'samplegroup'
sudo usermod -aG samplegroup $USER
sudo usermod -aG samplegroup testuser
echo "Users added to 'samplegroup'."

# Copy a local file to a remote host
scp /path/to/local/file.txt user@remotehost:/path/to/remote/directory/
echo "File has been copied to the remote host."

# Retrieve a file from a remote host to the local machine
scp user@remotehost:/path/to/remote/file.txt /path/to/local/directory/
echo "File has been retrieved from the remote host."

# Create a private file and set permissions
echo "Creating a private file..."
touch sensitive_data.txt
chmod 600 sensitive_data.txt
echo "Sensitive data protection set." # Expected action: File permissions set to owner only

# Downloading, unpacking, and "installing" a package
echo "Downloading and installing a package..."
wget -qO example.tar.gz http://example.com/example.tar.gz
tar -xzf example.tar.gz
echo "Package installed." # Expected output: Download and unpack messages

# Write system Date, Hostname, and Uptime to log
echo "Date: $(date)" > logs/system_info.txt
echo "Hostname: $(hostname)" >> logs/system_info.txt
echo "Uptime: $(uptime -p)" >> logs/system_info.txt

# Capture the most recent system logs
echo "Capturing recent system logs..."
sudo journalctl -n 10 > tmp_logs.txt # Copy recent 10 lines to a temporary log
echo -e "\nRecent System Logs:" >> logs/system_info.txt
cat tmp_logs.txt >> logs/system_info.txt # Transfer info from temporary log to main log
rm tmp_logs.txt # Remove temporary log file
echo "Recent system logs appended to logs/system_info.txt"

# Snapshot of top performance-heavy processes
echo "Grabbing top processes snapshot..."
top -b -n 1 | head -15 > logs/process_log.txt
echo "Top processes snapshot saved to logs/process_log.txt" # Expected action: Top processes info saved

# Multi-step command using awk, grep, sed
echo "Demonstrating awk/grep/sed usage..."
ps aux | grep 'bash' | awk '{print $2}' | sed 's/^/PID: /' > logs/process_log.txt
echo "Bash process PIDs logged." # Expected action: Bash process IDs logged with modification

# Job control example
echo "Starting a background job..."
sleep 60 &  # Starts a sleep command in the background
job_id=$! # Captures the Process ID of the last Job
echo "Background job started with ID: $job_id" # Expected output: Background job ID
kill $job_id # Kill the service
echo "Service (PID: $job_id) has been terminated."

# Start a long-running process (sleep for 100 seconds) in the background with nohup
nohup sleep 100 &> /dev/null &
echo "Long-running process started in the background with nohup."

# Assuming you have background jobs running, list them
jobs
fg %1 # This command will bring job 1 to the foreground, making it interactively controlled.

# Check the status of the SSH service
echo "Checking SSH service status..."
sudo systemctl status ssh | grep "Active:" > logs/system_info.txt
echo "SSH service status written to logs/service_status.txt" #

# Generate an RSA SSH key pair with a comment
ssh-keygen -t rsa -b 4096 -C "your_email@example.com" -f ~/.ssh/id_rsa -N ""
#Note: (-N "") leaves the passphrase empty for the key, however for security reasons, it's recommended to not use this flag, so that a passphrase can be set.
# Output the public key to the console for easy copying
cat ~/.ssh/id_rsa.pub

# Network restart and log (actual command commented out for safety)
echo "Restarting network interface (simulation)..." >> logs/network_log.txt
# sudo ifdown eth0 && sudo ifup eth0
echo "Network interface restarted." # Expected output: Network restart simulation message

# Check network connection status
echo "Checking network connection status..."
ping -c 4 example.com > /dev/null && echo "Network is up." || echo "Network is down."
# Expected output: "Network is up." or "Network is down."

# Ping a website to check connectivity
ping -c 4 example.com

# Run mtr to trace the route to example.com and show the results
mtr -r -c 1 example.com
# Output:
# HOST: your_local_machine              Loss%   Snt   Last   Avg  Best  Wrst StDev
#   1.|-- 192.168.1.1                    0.0%     1    1.2   1.2   1.2   1.2   0.0
#   2.|-- 10.0.0.1                       0.0%     1    2.4   2.4   2.4   2.4   0.0
#   3.|-- 203.0.113.1                    0.0%     1   10.5  10.5  10.5  10.5   0.0

# Assign a secondary IP address to the secondary network interface (eth1)
sudo ip addr add 192.168.1.100/24 dev eth1
sudo ip link set eth1 up # Bring the interface up
ip addr show eth1 # Check the current IP address
echo "Secondary IP configured and interface brought up."

# List current firewall Rules w/ UFW
echo "Current UFW firewall rules:"
sudo ufw status verbose
# Expected output: Lists all active rules

# Allowing incoming SSH traffic on port 22 w/ UFW
sudo ufw allow 22
echo "Incoming SSH traffic allowed."
# Expected output: Confirmation of rule addition

# Enabling IPtables service to start on boot and saving rules
# For systems using systemd
sudo systemctl enable iptables
sudo iptables-save > /etc/iptables/rules.v4
echo "IPtables service enabled on boot and rules saved."
# Expected output: Confirmation messages

# Blocking incoming traffic from a specific IP address w/ IPtables
sudo iptables -A INPUT -s 192.168.1.100 -j DROP
echo "Incoming traffic from 192.168.1.100 blocked."
# After configuring, don't forget to save:
sudo iptables-save > /etc/iptables/rules.v4
# Expected output: Confirmation of IP block

# Identify a new SSD (assuming /dev/sdb) and create a new partition table
echo "Creating a new GPT partition table on /dev/sdb..."
sudo parted /dev/sdb --script mklabel gpt
echo "Partition table created."

# Optionally, create a single partition covering the entire drive
sudo parted /dev/sdb --script mkpart primary ext4 1MiB 100%
echo "New partition created on /dev/sdb."
# Expected output: Confirmation of partition table and partition creation

# Create mount point and mount the SSD partition
sudo mkdir -p /mnt/ssd
sudo mount /dev/sdb1 /mnt/ssd

# Use rsync to copy logs directory to the SSD
rsync -av ~/script_demo/logs /mnt/ssd/
echo "Logs directory backed up to SSD."

# Use disk management commands to log SSD space info
echo "Logging SSD space information for /dev/sda and /dev/sdb..."
df -h | grep -E '/dev/sda|/dev/sdb' > logs/disk_log.txt
echo "SSD space information for both drives logged."

# List all block devices in a tree-like format
lsblk

# List block devices with additional details like the file system type, label, UUID, and mount point
lsblk -o NAME,FSTYPE,LABEL,UUID,MOUNTPOINT

# Pushing a Commit to Update the Logs
# Assuming logs are updated, add them to the staging area
git add logs/*.txt
echo "Logs added to staging area."

# Commit the update to the repository
git commit -m "Updated Logs"
echo "Log updates committed."

# Push the commit to the remote repository (assuming a remote named 'origin' is set up)
git push origin master
echo "Changes pushed to remote repository."

# (Virtualization) For Docker, a Dockerfile would include steps like:
# FROM ubuntu:latest
# COPY . /app
# RUN apt-get update && apt-get install -y cron
# CMD ["cron", "-f"]

# Schedule this script to run daily using cron (add this line to your crontab manually)
# 0 0 * * * /path/to/your/script.sh

# Final statement
echo "Script execution completed. Logs and other outputs have been generated."