Aug 2, 2021 8 min read

Using Checkmk for Monitoring Your Linux Server Infrastructure

A detailed guide on installing and configuring the free and open-source Checkmk Raw Edition for monitoring servers.
Table of Contents

There are tons of tools available for monitoring your IT infrastructure. This includes monitoring the Linux servers, containers, databases, applications and more.

Services like BetterUptime are convenient and we use it for downtime monitoring.

However, for more granular control, I prefer deploying tools like Prometheus with the beautiful Grafana dashboard.

Recently, I came across a project that gives a complete view of your IT infrastructure within a very short span of time.

Checkmk for monitoring IT infrastructure

Checkmk server monitoring dashboard

With Checkmk, you can effectively harness powerful monitoring capabilities to keep a watchful eye not only on servers, but also networks, clouds, containers, and applications.

Checkmk is available in two main editions. The managed enterprise edition costs money but it has more features.

It also has a free and open source edition called Checkmk Raw Edition (RE).

I am going to show how to deploy and set up Checkmk RE for monitoring your servers.

Setting up Checkmk RE for managing Linux servers

I am going to take you on a walkthrough of Checkmk RE and show how you can install, configure and finally use it. I've followed the official documentation and honestly found it quite more complex to configure compared to the earlier tools I had explored.

Therefore, I decided to focus on making that experience better through this article.

Before I begin, I would like to reiterate that, like Cockpit, installing a Docker version of Checkmk Raw Edition is not quite recommended in general practice.

Install Checkmk RE on the server you want to monitor

You need to have Checkmk RE and the Checkmk agent installed to be able to monitor your server. At this time of review, I have tested version 2.0.0p7.

Download the necessary package

For this tutorial, I'm going to first download Checkmk RE on an Ubuntu 20.04 server:

wget https://download.checkmk.com/checkmk/2.0.0p7/check-mk-raw-2.0.0p7_0.focal_amd64.deb

Verify the Checkmk package

Install dpkg-sig for package verification. Also make sure gpg is installed.

sudo apt -y install dpkg-sig gpg

After that is done, obtain the gpg key:

avimanyu@localhost:~$ gpg --keyserver keyserver.ubuntu.com --recv-keys 434DAC48C4503261
gpg: directory '/home/avimanyu/.gnupg' created
gpg: keybox '/home/avimanyu/.gnupg/pubring.kbx' created
gpg: /home/avimanyu/.gnupg/trustdb.gpg: trustdb created
gpg: key 434DAC48C4503261: public key "Check_MK Software Release Signing Key (2018) <feedback@check-mk.org>" imported
gpg: Total number processed: 1
gpg:               imported: 1
avimanyu@localhost:~$ gpg --armor --export 434DAC48C4503261 > Check_MK-pubkey.gpg

Add the newly obtained public key:

avimanyu@localhost:~$ sudo apt-key add Check_MK-pubkey.gpg
OK

Now you can verify the Checkmk package you just downloaded:

avimanyu@localhost:~$ dpkg-sig --verify check-mk-raw-2.0.0p7_0.focal_amd64.deb
Processing check-mk-raw-2.0.0p7_0.focal_amd64.deb...
GOODSIG _gpgbuilder B1E7106575B723F00611C612434DAC48C4503261 1625600497

GOODSIG indicates successful verification. So let us now proceed with the installation.

Install Checkmk Raw Edition

You can use apt to directly install the recently downloaded package:

sudo apt -y install ~/check-mk-raw-2.0.0p7_0.focal_amd64.deb

Just to be sure, for the sake of it, ensure the apache2 service is active and that port 80(used by Apache) is not already being used by some other service.

avimanyu@localhost:~$ systemctl status apache2
● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2021-07-14 17:30:18 UTC; 6s ago
       Docs: https://httpd.apache.org/docs/2.4/
    Process: 46288 ExecStart=/usr/sbin/apachectl start (code=exited, status=0/SUCCESS)
   Main PID: 46309 (apache2)
      Tasks: 55 (limit: 4617)
     Memory: 7.1M
     CGroup: /system.slice/apache2.service
             ├─46309 /usr/sbin/apache2 -k start
             ├─46310 /usr/sbin/apache2 -k start
             └─46311 /usr/sbin/apache2 -k start

Create your initial web user interface(UI) for first time access

Before you begin monitoring, you must first create your web UI with Open Monitoring Distribution (OMD).

What is the Open Monitoring Distribution?
The Open Monitoring Distribution (OMD) provides a precompiled monitoring solution with all important add-ons – and all of these preconfigured and well-matched to each other.

Here, I set the new site name as mysite:

avimanyu@localhost:~$ sudo omd create mysite
Adding /opt/omd/sites/mysite/tmp to /etc/fstab.
Creating temporary filesystem /omd/sites/mysite/tmp...OK
Updating core configuration...
Generating configuration for core (type nagios)...Precompiling host checks...OK
OK
Restarting Apache...OK
Created new site mysite with version 2.0.0p7.cre.

  The site can be started with omd start mysite.
  The default web UI is available at http://localhost/mysite/

  The admin user for the web applications is cmkadmin with password: KgjKy6wpR
  For command line administration of the site, log in with 'omd su mysite'.
  After logging in, you can change the password for cmkadmin with 'htpasswd etc/htpasswd cmkadmin'.

Once that is done, you'll receive important access credentials along-with some helpful instructions to get started with your new UI. I'd recommend saving the output in a separate document for safe-keeping.

If you have physical access to the server, you can use localhost in the web browser like this.

localhost/mysite

In either case, you can access the setup with your server's public IP address. For example, if its IP address is 1.2.3.4,  your access URL would be:

1.2.3.4/mysite

In case it has a domain name (say checkmk.domain.com), use:

checkmk.domain.com/mysite

Following that, you should see a login interface like this:

Using the credentials obtained after creating mysite, log into Checkmk. The default admin name as you might have noted, is cmkadmin.

Install Checkmk Agent

To be able to add hosts (servers) you must now install the Checkmk Agent via a package installation. The package download URL can be obtained by ensuring the following steps:

Navigate to Setup and choose Linux under the Agents submenu:

Navigating to the Checkmk Agent Linux Page from the Setup menu
Checkmk Agent for Linux on the Setup menu

Locate the Debian package(since I'm using Ubuntu):

The Debian Package(required for Ubuntu) is listed and linked under Packaged Agents on the Agent Linux Page
Locating the Debian Package(required for Ubuntu)

Right click and copy the URL on your browser(Firefox in this case):

Right click on the Debian package name and select "Copy Link" to fetch the Checkmk Agent download URL
Fetching the Download URL for the Checkmk Agent

Once you copy the URL, download it on the server with wget. Supposing the IP is 1.2.3.4, the corresponding command would be:

wget http://1.2.3.4/mysite/check_mk/agents/check-mk-agent_2.0.0p7-1_all.deb

Once the download is complete, install the agent package:

sudo apt -y install ~/check-mk-agent_2.0.0p7-1_all.deb

Now you are ready to add servers as hosts for monitoring activities on Checkmk.

Preparing Checkmk for monitoring your server(s)

Begin adding the host server based on each of the steps shared below.

Start at Setup > Hosts > Hosts.

Setting up Checkmk dashboard

Select “Add host to the monitoring”(repeat this step to add more servers).

Enter the Hostname as localhost and select “Save & go to connection tests”(Use server's public IP or domain name as Hostname for remote servers).

Wait for the connection tests to complete.

Once the tests get completed, click on “service discovery”.

Select “Fix all” to diagnose “Undecided services”.

Now click on “3 changes” located on the top right with the yellow circle having an exclamation mark. The number of changes may vary from user to user.

Select “Activate on selected sites”.

Wait for activation to complete.

After activation is complete, you'll notice “Success” within the progress bar that would eventually turn green:

Successful activation status of Checkmk
Checkmk Activation Status Page

At this stage, I'll log out and will log back in to reconfirm that the server that I just added is indeed now being monitored by Checkmk:

Logout of Checkmk via the Logout option from the User menu down below at the bottom left
Logging out of Checkmk

Monitoring your server(s) with Checkmk

On successfully logging back again, you'd notice a green hexagon revealing your newly added server on the main dashboard:

Checkmk Main Dashboard showing added server up and running
Checkmk Main Dashboard

Now, navigate to Monitor > System > Checkmk dashboard:

Navigating to the Checkmk dashboard from the Monitor > System submenu for a very brief monitoring overview of your server
Navigating to the Checkmk dashboard

Note that it's different from the Main dashboard seen earlier on first login after adding the host. On this Checkmk dashboard, you can see a very brief monitoring overview of your server. Click on localhost:

Once you click on it, you will finally see the generic monitoring page for a server, consisting of the commonly known metrics, namely:

  • CPU Load
  • Used RAM
  • Disk throughput
  • Filesystem size and used space
  • Major page faults
  • Average disk latency
  • Network

You have to navigate to this interface in the above described manner every time you wish to monitor your server. But, you can also create a bookmark based on the following URL to open it quickly for regular access:

http://localhost/mysite/check_mk/dashboard.py?host=localhost&name=checkmk_host&site=mysite

In the above URL, replace localhost with your own server's IP or domain. Also, replace mysite with the site name you set.

Bonus Tip: Metric Specific Monitoring

If you want to monitor server specific metrics in vivid detail, Checkmk's got you covered. For example, if you want to monitor CPU load or usage in-depth and individually, follow the below steps:

Navigate to Monitor > Overview > All hosts

"All hosts" can be accessed within the "Overview" submenu under the "Monitor" menu
Navigating to “All hosts” under Monitor > Overview submenu

Click on localhost:

The "All hosts" page allows access server metrics individually and in vivid detail
The “All hosts” page

Now click on “CPU load” or “CPU utilization”. Notice, there are so many other metrics for you to monitor on an individual basis.

The "Services of Hosts" page lists all accessible server metrics that can be monitored individually in detail
“Services of Host” allows access to server metrics individually and in vivid detail

Here, I've selected “CPU load”:

CPU load specific detailed metric on Checkmk allows monitoring CPU status based on a variety of time parameters.
CPU load specific detailed metric on Checkmk

As you can observe, this detailed metric on Checkmk allows monitoring CPU load based on a variety of time-based parameters.

I do hope you find this guide useful and try out this promising tool on your own, be it your server or even your desktop system. If you would like to add any feedback, thoughts or comments, please do so in the section below.

Avimanyu Bandyopadhyay
Avimanyu Bandyopadhyay
DevOps Geek at Linux Handbook. Doctoral Researcher on GPU-based Bioinformatics & author of 'Hands-On GPU Computing with Python'. He strongly believes in the significance of Linux and FOSS in Science.

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