Essential A to Z Command Guide for MongoDB, PostgreSQL, Linux & Git on Ubuntu VPS

MongoDB Commands (A to Z)

• Database Operations

# Connect to MongoDB shell
mongosh

# Switch or create a database
use your_db_name

# Show all databases
show dbs

# Show collections in current DB
show collections

• CRUD (Create, Read, Update, Delete)

# Insert one document
db.users.insertOne({ name: "John", age: 30 })

# Insert many
db.users.insertMany([{name: "A"}, {name: "B"}])

# Read all documents
db.users.find()

# Filtered query
db.users.find({ name: "John" })

# Update document
db.users.updateOne({ name: "John" }, { $set: { age: 31 } })

# Delete one document
db.users.deleteOne({ name: "John" })

# Delete many documents
db.users.deleteMany({})

• Indexes, Users

# Create index
db.users.createIndex({ name: 1 })

# Create new user
db.createUser({
  user: "admin",
  pwd: "securepassword",
  roles: [{ role: "readWrite", db: "your_db_name" }]
})

PostgreSQL Commands (A to Z)

• Login and Setup

# Login to postgres
psql -U postgres

# List all databases
\l

# Connect to a database
\c your_db

# List tables
\dt

• CRUD SQL

-- Create table
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  name TEXT,
  age INT
);

-- Insert
INSERT INTO users (name, age) VALUES ('John', 30);

-- Select
SELECT * FROM users;

-- Update
UPDATE users SET age = 31 WHERE name = 'John';

-- Delete
DELETE FROM users WHERE name = 'John';

• Admin & Users

-- Create user
CREATE USER myuser WITH PASSWORD 'mypassword';

-- Grant privileges
GRANT ALL PRIVILEGES ON DATABASE your_db TO myuser;

Linux (Ubuntu) Commands (A to Z)

• Navigation

pwd                 # Show current directory
ls                  # List files/folders
cd folder_name      # Change directory
cd ..               # Go back one directory

• File Handling

touch file.txt                # Create empty file
mkdir my_folder               # Create folder
cp file.txt copy.txt          # Copy file
mv file.txt folder/           # Move file
rm file.txt                   # Remove file
rm -r folder_name             # Delete folder

• System Info

whoami              # Current user
uname -a            # System info
df -h               # Disk usage
free -m             # RAM usage
uptime              # System uptime

• Networking

ip a                        # Show IP addresses
ping google.com             # Ping test
netstat -tulpn              # Listening ports
curl ifconfig.me            # Public IP

• Package Management

sudo apt update             # Update package list
sudo apt upgrade            # Upgrade packages
sudo apt install nginx      # Install a package
sudo apt remove nginx       # Remove a package

• Permissions

chmod +x file.sh            # Make script executable
chown user:user file        # Change ownership
sudo -i                     # Switch to root

Git Commands (A to Z)

• Project Setup

git init                            # Initialize git repo
git clone https://url.com/project  # Clone repo
git remote add origin URL          # Add remote

• Committing Changes

git status              # Show changes
git add .               # Stage all changes
git commit -m "Message" # Commit

• Branching

git branch                     # List branches
git checkout -b new-branch     # Create and switch
git checkout main              # Switch branch
git merge branch-name          # Merge branch

• Push & Pull

git push -u origin main        # Push to main
git pull origin main           # Pull latest

Server Management

• Services

sudo systemctl start nginx      # Start service
sudo systemctl stop nginx       # Stop service
sudo systemctl restart nginx    # Restart service
sudo systemctl status nginx     # Service status

• Crontab (Scheduled Jobs)

crontab -e                     # Edit cron jobs
* * * * * /path/to/script.sh   # Every minute

Useful Tools to Install on Ubuntu

sudo apt install git
sudo apt install curl
sudo apt install build-essential
sudo apt install nodejs npm
sudo apt install mongodb
sudo apt install postgresql

Other Essentials

history         # Show all previous commands
alias gs="git status"  # Create alias
reboot          # Reboot server
shutdown now    # Power off server