How To Install Graylog on CentOS 7

About Graylog Components

Graylog has four main components:

• Graylog Server nodes: Serves as a worker that receives and processes messages, and communicates with all other non-server components. Its performance is CPU dependent
• Elasticsearch nodes:
• Stores all of the logs/messages. Its performance is RAM and disk I/O dependent
• MongoDB: Stores metadata and does not experience much load
• Web Interface: The user interface

This tutorial will implement a very basic Graylog setup, with all of the components installed on the same server. 
For a larger, production setup, it is advisable to set up install the components on separate servers.

Install MongoDB 

The MongoDB installation is simple and quick. Run the following command to import the MongoDB public GPG key into rpm:

sudo rpm --import https://www.mongodb.org/static/pgp/server-3.2.asc

Create the MongoDB source list:

echo '[mongodb-org-3.2] name=MongoDB Repository baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.2/x86_64/ gpgcheck=1 enabled=1' | sudo tee /etc/yum.repos.d/mongodb-org-3.2.repo

Install the latest stable version of MongoDB with this command:

sudo yum install -y mongodb-org
Now start MongoDB:

sudo systemctl restart mongod

MongoDB should be up and running now. Let's move on to installing Java.

Install Java 
Elasticsearch and Logstash require Java, so we will install that now. We will install a recent version of Oracle Java 8 because that is what Elasticsearch recommends. It should, however, work fine with OpenJDK, if you decide to go that route. Following the steps in this section means that you accept the Oracle Binary License Agreement for Java SE. Change to your home directory and download the Oracle Java 8 (Update 73, the latest at the time of this writing) JDK RPM with these commands:

wget --no-cookies --no-check-certificate --header "Cookie: gpw_e24=http%3A%2F%2Fwww.oracle.com%2F; oraclelicense=accept-securebackup-cookie" "http://download.oracle.com/otn-pub/java/jdk/8u73-b02/jdk-8u73-linux-x64.rpm"

Then install the RPM with this yum command (if you downloaded a different release, substitute the filename here):

sudo yum -y localinstall jdk-8u73-linux-x64.rpm

Now Java should be installed at /usr/java/jdk1.8.0_73/jre/bin/java, and linked from /usr/bin/java.

you may delete the archive file that you downloaded earlier:

rm ~/jdk-8u*-linux-x64.rpm

Now that Java is installed, let's install Elasticsearch.

Install Elasticsearch Graylog 1.x only works with pre-2.0 versions of Elasticsearch, so we will install Elasticsearch 1.7.x. Elasticsearch can be installed with a package manager by adding Elastic's package source list. Run the following command to import the Elasticsearch public GPG key into rpm:

sudo rpm --import http://packages.elastic.co/GPG-KEY-elasticsearch

Create a new yum repository file for Elasticsearch by running this command:

echo '[elasticsearch-1.7] name=Elasticsearch repository for 1.7.x packages baseurl=http://packages.elastic.co/elasticsearch/1.7/centos gpgcheck=1 gpgkey=http://packages.elastic.co/GPG-KEY-elasticsearch enabled=1' | sudo tee /etc/yum.repos.d/elasticsearch.repo

Install Elasticsearch with this command:

sudo yum -y install elasticsearch

Elasticsearch is now installed. Let's edit the configuration:
sudo vi /etc/elasticsearch/elasticsearch.yml

Find the section that specifies cluster.name. Uncomment it, and replace the default value with "graylog-development", so it looks like the following:

cluster.name: graylog-development

You will want to restrict outside access to your Elasticsearch instance (port 9200), so outsiders can't read your data or shutdown your Elasticsearch cluster through the HTTP API. Find the line that specifies network.host, uncomment it, and replace its value with "localhost" so it looks like this:
network.host: localhost

Save and exit elasticsearch.yml.

Now start Elasticsearch:

sudo systemctl restart elasticsearch

Then run the following command to start Elasticsearch on boot up:
sudo systemctl enable elasticsearch

After a few moments, run the following to test that Elasticsearch is running properly:
curl -XGET 'http://localhost:9200/_cluster/health?pretty=true'

Now that Elasticsearch is up and running, let's install the Graylog server.

Install Graylog Server

Now that we have installed the other required software, let's install the server component of Graylog, graylog-server.

First, download the Graylog RPM package to your system with this command:
sudo rpm -Uvh https://packages.graylog2.org/repo/packages/graylog-1.3-repository-el7_latest.rpm

Then install the graylog-server package with these commands:
sudo yum -y install graylog-server

Install pwgen, which we will use to generate password secret keys:
sudo yum -y install epel-release 
sudo yum -y install pwgen

Now we must configure the admin password and secret key. The password secret key is configured in server.conf, by the password_secret parameter. We can generate a random key and insert it into the

Graylog configuration with the following two commands:
SECRET=$(pwgen -s 96 1) 

sudo -E sed -i -e 's/password_secret =.*/password_secret = '$SECRET'/' /etc/graylog/server/server.conf



The admin password is assigned by creating an shasum of the desired password, and assigning it to the root_password_sha2 parameter in the Graylog configuration file. Create shasum of your desired password with the following command, substituting the highlighted "password" with your own. The sed command inserts it into the Graylog configuration for you:

PASSWORD=$(echo -n password | sha256sum | awk '{print $1}')
sudo -E sed -i -e 's/root_password_sha2 =.*/root_password_sha2 = '$PASSWORD'/' /etc/graylog/server/server.conf

Now that the admin password is setup, let's open the Graylog configuration to make a few changes:
sudo vi /etc/graylog/server/server.conf

You should see that password_secret and root_password_sha2 have random strings to them because of the commands that you ran in the steps above.

Now we will configure the rest_transport_uri, which is how the Graylog web interface will
communicate with the server. Because we are installing all of the components on a single server, let's set the value to 127.0.0.1, or localhost. Find and uncomment rest_transport_uri, and change it's value so it looks like the following:

/etc/graylog/server/server.conf
rest_transport_uri = http://127.0.0.1:12900/

Next, because we only have one Elasticsearch shard (which is running on this server), we will change the value of elasticsearch_shards to 1:

/etc/graylog/server/server.conf
elasticsearch_shards = 1

Next, change the value of elasticsearch_cluster_name to "graylog-development" (the same as the Elasticsearch cluster.name):

/etc/graylog/server/server.conf
elasticsearch_cluster_name = graylog-development

Uncomment these two lines to discover the Elasticsearch instance using unicast instead of multicast:
/etc/graylog/server/server.conf

elasticsearch_discovery_zen_ping_multicast_enabled = false
elasticsearch_discovery_zen_ping_unicast_hosts = 127.0.0.1:9300

Save and quit. Now graylog-server is configured and ready to be started.

Start the Graylog server with the service command:
sudo systemctl start graylog-server

The next step is to install the Graylog web interface. Let's do that now!

Install Graylog Web

Install Graylog Web with this command:
sudo yum -y install graylog-web

Next, we want to configure the web interface's secret key, the application.secret parameter in web.conf. We will generate another key, as we did with the Graylog server configuration, and insert it with sed, like so:
SECRET=$(pwgen -s 96 1)
sudo -E sed -i -e 's/application\.secret=""/application\.secret="'$SECRET'"/' /etc/graylog/web/web.conf

Now open the web interface configuration file, with this command:
sudo vi /etc/graylog/web/web.conf

Now we need to update the web interface's configuration to specify the graylog2-server.uris parameter. This is a comma delimited list of the server REST URIs. Since we only have one Graylog server node, the value should match that of rest_listen_uri in the Graylog server configuration (i.e. "http://127.0.0.1:12900/").

/etc/graylog/web/web.conf excerpt
graylog2-server.uris="http://127.0.0.1:12900/"

The Graylog web interface is now configured. Start the Graylog web interface:
sudo systemctl restart graylog-web

Now we can use the Graylog web interface. Let's do that now.

Configure Graylog to Receive syslog messages

Log into Graylog Web Interface
In your favorite web browser, go to the port 9000 of your server's public IP address:

http://graylog_public_IP:9000/

You should see a login screen. Enter admin as your username and the admin password that you set earlier.

Once logged in, you will see something like the following:

The red number at the top is a notification. If you click on it, you will see a message that says you have a node without any running inputs. Let's add an input to receive syslog messages over UDP now.

Create Syslog UDP Input

To add an input to receive syslog messages, click on the System drop-down in the top menu.
Now, from the drop-down menu, select Inputs.
Select Syslog UDP from the drop-down menu and click the Launch new input button.

A "Launch a new input: Syslog UDP" modal window will pop up. Enter the following information (substitute in your server's private IP address for the bind address):

Title: syslog
Port: 8514
Bind address: graylog_private_IP

Then click Launch.

You should now see an input named "syslog" in the Local inputs section (and it should have a green box that says "running" next to it), like so:

Now our Graylog server is ready to receive syslog messages on port 8514 from your servers. Let's configure your servers to send their syslog messages to Graylog now.

Configure Rsyslog to Send Syslogs to Graylog Server

On all of your client servers, the servers that you want to send syslog messages to Graylog, do the following steps.

Create an rsyslog configuration file in /etc/rsyslog.d. We will call ours 90-graylog.conf:
sudo vi /etc/rsyslog.d/90-graylog.conf

In this file, add the following lines to configure rsyslog to send syslog messages to your Graylog server (replace graylog_private_IP with your Graylog server's private IP address):

/etc/rsyslog.d/90-graylog.conf
$template GRAYLOGRFC5424,"<%pri%>%protocol-version% %timestamp:::date-rfc3339% %HOSTNAME% %app-name% %procid% %msg%\n"
 *.* @graylog_private_IP:8514;GRAYLOGRFC5424

Save and quit. This file will be loaded as part of your rsyslog configuration from now on. Now you need to restart rsyslog to put your change into effect.
sudo systemctl restart rsyslog

After you are finished configuring rsyslog on all of the servers you want to monitor, go back to the Graylog web interface.

Viewing Your Graylog Sources

In your favorite web browser, go to the port 9000 of your server's public IP address:

http://graylog_public_IP:9000/

Click on Sources in the top bar. You will see a list of all of the servers that you configured rsyslog on. 
 The hostname of the sources is on the left, with the number of messages received by Graylog on the right.

Searching Your Graylog Data

After letting your Graylog collect messages for some time, you will be able to search through the messages. As an example, let's search for "sshd" to see what kind of SSH activity is happening on our servers. Here is a snippet of our results:

As you can see, our example search results revealed sshd logs for various servers, and a lot of failed root login attempts. Your results may vary, but it can help you to identify many issues, including how unauthorized users are attempting to access your servers.

in addition to the basic search functionality on all of your sources, you can search the logs of a specific host, or in a specific time frame. Searching through data in Graylog is useful, for example, if you would like to review the logs of a server or several servers after an incident has occurred. Centralized logging makes it easier to correlate related incidents because you do not need to log into multiple servers to see all the events that have happened.

 For more information on how the search bar works, check out the official documentation: Graylog Searching

Good luck!