Introduction
MongoDB is a document-oriented database that is free and open-source. It is classified as a NoSQL database because it does not rely on a traditional table-based relational database structure. Instead, it uses JSON-like documents with dynamic schemas. Unlike relational databases, MongoDB does not require a predefined schema before you add data to a database. You can alter the schema at any time and as often as is necessary without having to set up a new database with an updated schema.
In this tutorial, you will install MongoDB Community Edition on a CentOS 7 server.
Prerequisites
Before following this tutorial, make sure you have
A CentOS 7 server with a non-root sudo-enabled user. For guidance, please see our tutorial, Initial Server Setup with CentOS 7.
Step 1 – Adding the MongoDB Repository
The mongodb-org package does not exist within the default repositories for CentOS. However, MongoDB maintains a dedicated repository. Let’s add it to our server.
With the vi editor, create a .repo file for yum, the package management utility for CentOS:
sudo vi /etc/yum.repos.d/mongodb-org.repo
Then, visit the Install on Red Hat section of MongoDB’s documentation and add the repository information for the latest stable release to the file:
/etc/yum.repos.d/mongodb-org.repo
[mongodb-org-6.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/6.0/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-6.0.asc
Save the changes to the file by pressing the ESC key, then type :wq, and hit ENTER.
Before continuing, you should verify that the MongoDB repository exists within the yum utility. The repolist command displays a list of enabled repositories:
yum repolist
. . .
repo id repo name
base/7/x86_64 CentOS-7 - Base
extras/7/x86_64 CentOS-7 - Extras
mongodb-org-6.0/7/x86_64 MongoDB Repository
updates/7/x86_64 CentOS-7 - Updates
. . .
With the MongoDB Repository in place, you can proceed with the installation.
Step 2 – Installing MongoDB
You can install the mongodb-org package from the third-party repository using the yum utility.
sudo yum install mongodb-org
There are two Is this ok [y/N]: prompts. The first one permits the installation of the MongoDB packages and the second one imports a GPG key. The publisher of MongoDB signs their software and yum uses a key to confirm the integrity of the downloaded packages. At each prompt, type Y and then press the ENTER key.
Next, start the MongoDB service with the systemctl utility:
sudo systemctl start mongod
Although we will not use them in this tutorial, you can also change the state of the MongoDB service with the reload and stop commands.
The reload command requests that the mongod process reads the configuration file, /etc/mongod.conf, and applies any changes without requiring a restart.
sudo systemctl reload mongod
The stop command halts all running mongod processes.
sudo systemctl stop mongod
The systemctl utility did not provide a result after executing the start command, but you can check that the service started by viewing the end of the mongod.log file with the tail command:
sudo tail /var/log/mongodb/mongod.log
. . .
[initandlisten] waiting for connections on port 27017
An output of waiting for a connection confirms that MongoDB has started successfully and you can access the database server with the MongoDB Shell:
mongo
Note: When you launched the MongoDB Shell, you may have seen a warning like this:
** WARNING:** soft rlimits too low. rlimits set to 4096 processes, 64000 files. Number of processes should be at least 32000 : 0.5 times number of files.
MongoDB is a threaded application. It can launch additional processes to handle its workload. The warning states that for MongoDB to be most effective the number of processes that it is authorized to spin up should be half that of the number of files that it can have open at any given time. To resolve the warning, alter the processes soft rlimit value for mongod by editing the 20-nproc.conf file:
sudo vi /etc/security/limits.d/20-nproc.conf
Add the following line to the end of file:
/etc/security/limits.d/20-nproc.conf
. . .
mongod soft nproc 32000
Make sure to save the changes pressing the ESC key, then type :wq, and hit ENTER.
For the new limit to be available to MongoDB, restart it using the systemctl utility:
sudo systemctl restart mongod
Afterward, when you connect to the MongoDB Shell, the warning should cease to exist.
To learn how to interact with MongoDB from the shell, you can review the output of the db.help() method which provides a list of methods for the db object.
db.help()
DB methods:
db.adminCommand(nameOrDocument) - switches to 'admin' db, and runs command [ just calls db.runCommand(...) ]
db.auth(username, password)
db.cloneDatabase(fromhost)
db.commandHelp(name) returns the help for the command
db.copyDatabase(fromdb, todb, fromhost)
db.createCollection(name, { size : ..., capped : ..., max : ... } )
db.createUser(userDocument)
db.currentOp() displays currently executing operations in the db
db.dropDatabase()
. . .
Leave the mongod process running in the background, but quit the shell with the exit command:
exit
Bye
Step 3 – Verifying Startup
Because a database-driven application cannot function without a database, we’ll make sure that the MongoDB daemon, mongod, will start with the system.
Use the systemctl utility to check its startup status:
systemctl is-enabled mongod; echo $?
An output of zero confirms an enabled daemon, which we want. A one, however, confirms a disabled daemon that will not start.
. . .
enabled
0
In the event of a disabled daemon, use the systemctl utility to enable it:
sudo systemctl enable mongod
You now have a running instance of MongoDB that will automatically start following a system reboot.
Step 4 – Importing an Example Dataset (Optional)
Unlike other database servers, MongoDB does not come with data in its test database. Since we don’t want to experiment with new software using production data, we will download a sample dataset from a MongoDB example. This JSON document contains a collection of restaurants, which we’ll use to practice interacting with MongoDB and avoid causing harm to sensitive data.
Start by moving into a writable directory:
cd /tmp
Use the curl command and the link from MongoDB to download the JSON file:
curl -LO https://raw.githubusercontent.com/mongodb/docs-assets/primer-dataset/primer-dataset.json
The mongoimport command will insert the data into the test database. The --db flag defines which database to use while the --collection flag specifies where in the database the information will be stored, and the --file flag tells the command which file to perform the import action on:
mongoimport --db test --collection restaurants --file /tmp/primer-dataset.json
The output confirms the importing of the data from the primer-dataset.json file:
connected to: localhost
imported 25359 documents
With the sample dataset in place, you can perform a query against it.
Relaunch the MongoDB Shell:
mongo
The shell selects the test database by default, which is where you imported the data.
Query the restaurants collection with the find() method to display a list of all the restaurants in the dataset. Since the collection contains over 25,000 entries, use the optional limit() method to reduce the output of the query to a specified number. Additionally, the pretty() method makes the information more human-readable with newlines and indentations.
db.restaurants.find().limit(1).pretty()
{
"_id" : ObjectId("57e0443b46af7966d1c8fa68"),
"address" : {
"building" : "1007",
"coord" : [
-73.856077,
40.848447
],
"street" : "Morris Park Ave",
"zipcode" : "10462"
},
"borough" : "Bronx",
"cuisine" : "Bakery",
"grades" : [
{
"date" : ISODate("2014-03-03T00:00:00Z"),
"grade" : "A",
"score" : 2
},
{
"date" : ISODate("2013-09-11T00:00:00Z"),
"grade" : "A",
"score" : 6
},
{
"date" : ISODate("2013-01-24T00:00:00Z"),
"grade" : "A",
"score" : 10
},
{
"date" : ISODate("2011-11-23T00:00:00Z"),
"grade" : "A",
"score" : 9
},
{
"date" : ISODate("2011-03-10T00:00:00Z"),
"grade" : "B",
"score" : 14
}
],
"name" : "Morris Park Bake Shop",
"restaurant_id" : "30075445"
}
You can continue using the sample dataset to familiarize yourself with MongoDB or delete it with the db.restaurants.drop() method:
db.restaurants.drop()
Lastly, quit the shell with the exit command:
exit
Bye
Conclusion
In this tutorial, you added a third-party repository to yum, installed the MongoDB database server, imported a sample dataset, and performed a simple query. There is still much more you can do with MongoDB, such as creating databases with collections, filling databases with many documents, and building robust applications. To learn more about MongoDB, check our our series How To Manage Databases with MongoDB or our other tutorials on MongoDB.
