Steps to Resolve the Error

1. Remove Existing MongoDB Installation

First of all, make sure we completely remove any existing installation of MongoDB so as to avoid conflicts.

sudo apt-get purge mongodb-org*
sudo apt-get autoremove
sudo rm -r /var/log/mongodb
sudo rm -r /var/lib/mongodb

2. Import the MongoDB Public Key:

• Ensure that the necessary packages are installed by running the following command:

sudo apt-get install gnupg curl

• Then, import the MongoDB public GPG key with the following command:

curl -fsSL https://www.mongodb.org/static/pgp/server-7.0.asc | \
sudo gpg -o /usr/share/keyrings/mongodb-server-7.0.gpg \
--dearmor

3. Create a List File for MongoDB:

• Depending on our Ubuntu version, create the appropriate list file. For example, for Ubuntu 22.04 (Jammy), run:

echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-7.0.gpg ] https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/7.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-7.0.list

4. Reload Local Package Database:

• Update the local package database with the command:

sudo apt-get update

5. Install MongoDB Packages:

• Install the MongoDB package by executing:

sudo apt-get install -y mongodb-org

6. Start MongoDB Service:

• After installation, start the MongoDB service:

sudo systemctl start mongod

• If we encounter the error again “Failed to start mongod.service: Unit mongod.service not found ” run:

sudo systemctl daemon-reload

• Then try starting the service again.

7. Verify MongoDB Service Status:

• Check the status of the MongoDB service to ensure it has started successfully:

sudo systemctl status mongod

8. Optional: Enable Automatic Start on Boot:

• To ensure MongoDB starts automatically on system boot, enable the service:

sudo systemctl enable mongod

9. Additional Operations:

• Stop MongoDB: If needed, stop the MongoDB service using:

sudo systemctl stop mongod

• Restart MongoDB: Restart the MongoDB service with

sudo systemctl restart mongod

• Monitoring MongoDB Logs: Keep an eye on the MongoDB logs for any errors or important messages:
• tail -f /var/log/mongodb/mongod.log

10. Begin Using MongoDB:

• Start a mongosh session to interact with MongoDB:

mongosh

MongoDB a popular NoSQL database is famous for its flexibility and scalability. However, Ubuntu users may occasionally face difficulties when starting the MongoDB service, often encountering the error message: “Failed to start mongod.service: Unit mongod.service not found.”

In this article, We will learn about mongod.service: Unit mongod.service not found through troubleshooting and reinstalling MongoDB to resolve this issue efficiently.

Understanding the Error

• The message “Failed to start mongod.service: Unit mongod.service not found” means that either MongoDB is incorrectly installed or its configuration files are missing or damaged.
• For that reason, it cannot run which is crucial when working with MongoDB.

Common Causes

• Incomplete Installation: The installation of MongoDB may have been incomplete.
• Missing Service File: Missing or corrupted systemd service file for MongoDB.
• Outdated Package Database: Recognition issues may arise due to outdated local package database.