MongoDB installation and setup - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding MongoDB default port

What is the default port number MongoDB server listens on after installation?

A 27017

B 3306

C 8080

D 5432

💡 Hint

Think about the standard port MongoDB uses, different from MySQL or PostgreSQL.

MongoDB by default listens on port 27017. Ports 3306 and 5432 are for MySQL and PostgreSQL respectively, and 8080 is commonly used for web servers.

❓ query_result

intermediate

Check MongoDB service status command output

After installing MongoDB on a Linux system, you run systemctl status mongod. What output indicates the service is running correctly?

A Active: inactive (dead)

B Active: active (running) since ...

C Failed to start mongod.service: Unit not found.

D Active: activating (start) since ...

💡 Hint

Look for the word that means the service is currently working.

The status line showing active (running) means MongoDB is running properly. Other statuses indicate stopped, failed, or starting states.

📝 Syntax

advanced

Correct command to start MongoDB manually

Which of the following commands correctly starts the MongoDB server manually on a Linux system?

A sudo systemctl start mongod

B sudo mongod --start

C mongod start

D service mongod run

💡 Hint

Use the standard Linux service manager command.

The correct way to start MongoDB service is using systemctl start mongod. Other commands are either invalid or incorrect syntax.

🔧 Debug

advanced

Troubleshooting MongoDB connection error

You installed MongoDB and started the service, but when running mongo shell, you get Failed to connect to 127.0.0.1:27017. What is the most likely cause?

A MongoDB is listening on port 3306

B Firewall is blocking port 5432

C Mongo shell command is misspelled

D MongoDB service is not running

💡 Hint

Check if the server process is active before connecting.

If the MongoDB service is not running, the shell cannot connect to the default port 27017. Ports 3306 and 5432 are unrelated, and the shell command is correct.

❓ optimization

expert

Optimizing MongoDB startup for production

Which startup option improves MongoDB performance by enabling journaling and limiting memory usage?

A mongod --journal --cacheSize 8GB

B mongod --nojournal --cacheSize 4GB

C mongod --journal --wiredTigerCacheSizeGB 2

D mongod --nojournal --wiredTigerCacheSizeGB 1

💡 Hint

Journaling helps data safety; cache size controls memory use.

Option C enables journaling for data durability and sets WiredTiger cache size to 2GB, balancing performance and memory. Other options disable journaling or use invalid flags.

Practice

1. What is the first step to use MongoDB on your computer?

easy

A. Install MongoDB software

B. Create a database

C. Write queries

D. Connect to the internet

Solution

1. Step 1: Understand MongoDB setup process

   Before using MongoDB, you must have the software installed on your machine.

2. Step 2: Identify the initial action

   Installing MongoDB is the first step before creating databases or running queries.

3. Final Answer:

   Install MongoDB software -> Option A

4. Quick Check:

   First step = Install MongoDB software [OK]

Hint: Always install MongoDB before using it [OK]

Common Mistakes:

• Trying to create database before installation
• Assuming internet connection is needed first

2. Which command starts the MongoDB server on a local machine?

easy

A. mongod

B. mongo start

C. start mongo

D. mongo --start

Solution

1. Step 1: Recall MongoDB server start command

   The MongoDB server is started using the mongod command in the terminal.

2. Step 2: Check other options

   Options like mongo --start or mongo start are incorrect commands.

3. Final Answer:

   mongod -> Option A

4. Quick Check:

   Server start command = mongod [OK]

Hint: Use 'mongod' to start the MongoDB server [OK]

Common Mistakes:

• Using 'mongo' instead of 'mongod'
• Adding extra flags incorrectly

3. After installing MongoDB and starting the server, which command opens the MongoDB shell?

medium

A. mongod

B. mongo

C. start mongo

D. mongoshell

Solution

1. Step 1: Identify the shell command

   The MongoDB shell is accessed by running the mongo command after the server is running.

2. Step 2: Verify other options

   mongod starts the server, not the shell; others are invalid commands.

3. Final Answer:

   mongo -> Option B

4. Quick Check:

   Shell command = mongo [OK]

Hint: Use 'mongo' to open the MongoDB shell [OK]

Common Mistakes:

• Confusing 'mongod' with 'mongo'
• Typing invalid commands like 'mongoshell'

4. You tried to start MongoDB server with mongo command but got an error. What is the likely cause?

medium

A. MongoDB is not installed

B. MongoDB server is already running

C. You used the shell command instead of the server command

D. You need to connect to internet first

Solution

1. Step 1: Understand command roles

   mongo opens the shell, it does not start the server.

2. Step 2: Identify the error cause

   Using mongo to start the server causes an error because the server needs mongod.

3. Final Answer:

   You used the shell command instead of the server command -> Option C

4. Quick Check:

   Server start requires 'mongod', not 'mongo' [OK]

Hint: Use 'mongod' to start server, 'mongo' for shell [OK]

Common Mistakes:

• Using 'mongo' to start server
• Assuming internet is needed
• Ignoring installation status

5. You installed MongoDB and started the server with mongod. Now you want to connect to a specific database named shopDB using the shell. Which command should you run?

hard

A. mongosh --database shopDB

B. mongod shopDB

C. mongo --db shopDB

D. mongo shopDB

Solution

1. Step 1: Recall how to connect to a database in shell

   To connect to a specific database, you use mongo databaseName.

2. Step 2: Check other options

   mongod starts server, not shell; mongosh is a newer shell but mongosh --database shopDB uses wrong flag; mongo --db shopDB is invalid syntax.

3. Final Answer:

   mongo shopDB -> Option D

4. Quick Check:

   Connect to DB = mongo shopDB [OK]

Hint: Use 'mongo databaseName' to connect to a DB [OK]

Common Mistakes:

• Using 'mongod' to connect
• Wrong flags with 'mongosh'
• Assuming '--db' flag works