How to Install and Configure Monit on Linux Systems

In this article, I’ll show you how to install and configure monit  “servers and processes monitoring tool” on Linux systems (RPM Family “Redhat / CentOS  / Scientific Linux” and Debian Family “Debian / Ubuntu”). Monit has capability to monitor any service running on a Linux system, We only need to add settings for this service to monit. This article will help you to monitor the local running processes on your Linux machine and try to start the crashed processes.

So, What is Monit?

Monit ( A Process and Services Monitoring Tool) is a small Open Source utility for monitoring and managing Unix like systems. Monit monitors the server programs to increase services up-time and ensures that they stay online consistently. It’ll try to start any crashed service it monitors for a certain number of tries. You can tell Monit exactly what you would do if a program stops running, or begins using too much RAM, or another host becomes unreachable.

With Monit you get:

• Automatic process maintenance in a lightweight package.
• Capability to act on out-of-bounds values for CPU, RAM, disk, file size, age and more.
• Monitoring of running services, and the ability to start, kill or restart.
• Automatic email alerts sent at event triggers.
• Web interface for status monitoring.
• Availability from main package repositories.

Part 1: Installing Monit Server

Monit can be easily installed with package manager in most of Linux flavors.

• On CentOS, RHEL, Fedora and Scientific Linux

We need to enable  the epel repository in his system before installing it. run the following commands:

# yum -y install epel-release
# yum -y install monit

Now, we need to enable and start monit, run the following commands

On CentOS/RHEL 7

# systemctl enable monit 
# systemctl start monit

On CentOS/RHEL 6 and earlier

# chkconfig monit on 
# service monit start

• On Debian / Ubuntu

# apt-get -y install monit

Now, after we installed and run the monit, it’s time to configure it monitor some services.

Part 2: Enabling Web Interface in Monit

Monit also provided an web interface to view services and processes status. To enable monit web interface, edit configuration file ( For CentOS/RHEL 6 based /etc/monit.conf & For CentOS/RHEL 7 based /etc/monitrc & For Dabian Based System /etc/monit/monitrc ) in your favorite editor and uncomment following lines

set httpd port 2812 and
    use address localhost
    allow localhost
    allow admin:monit
    allow @monit
    allow @users readonly

And restart monit service.

# service monit restart

As per above configuration monit will start on port 2812 and only accessible from localhost. To change default port simply update first line of above showing configuration and set your preferred port.

Hint:
1. Enabling the web interface is important for monit cli to work, even if you do not have a gui on your server.

Part 3: Configuring Monit To Monitor Services

Now, it’s time to add services to monit. By default when we start monit it’ll monitor the machine it installed on, run the following commands to check the status of monit:

# monit status
The Monit daemon 5.14 uptime: 0m

 System 'SemariLabs00'
 status Running
 monitoring status Monitored
 load average [0.00] [0.00] [0.00]
 cpu 0.0%us 0.0%sy 0.0%wa
 memory usage 126.7 MB [12.8%]
 swap usage 0 B [0.0%]
 data collected Mon, 17 Oct 2016 12:03:57

Also, run the following command to get the summary of monit:

# monit summary
The Monit daemon 5.14 uptime: 0m

System 'SemariLabs00' Running

From the above outputs, monit is up, running, and by default monitors the host it installed on.

Let’s start with adding services to Monit. I’ll create a configuration file for each service I need to add to monit

• Monitoring apache web server

On CentOS / RHEL

Create the service configuration file in “/etc/monit.d/” as the following:

# vim /etc/monit.d/apache

Then add the following lines, and save then exit

check process apache with pidfile /var/run/httpd/httpd.pid 
    start program = "/etc/init.d/httpd start" with timeout 60 seconds
    stop program  = "/etc/init.d/httpd stop"

On Dabian / Ubuntu

Create the service configuration file in “/etc/monit/conf.d/” as the following:

# vim /etc/monit/conf.d/apache

Then add the following lines, and save then exit

check process apache with pidfile /run/apache2.pid
    start program = "/etc/init.d/apache2 start" with timeout 60 seconds
    stop program  = "/etc/init.d/apache2 stop"

Now restart monit service, run the following command

# service monit restart

And check the status of service using command line:

# monit summary
The Monit daemon 5.14 uptime: 0m 

Process 'apache' Running
System 'SemariLabs00' Running

•  Monitoring MySQL/MariaDB database server
  

On CentOS / RHEL

Create the service configuration file in “/etc/monit.d/” as the following:

# vim /etc/monit.d/mysql

Then add the following lines, and save then exit

check process mysqld with pidfile /var/run/mysqld/mysqld.pid
    start program = "/etc/init.d/mysql start"
    stop program = "/etc/init.d/mysql stop"

On Dabian / Ubuntu

Create the service configuration file in “/etc/monit/conf.d/” as the following:

# vim /etc/monit/conf.d/mysql

Then add the following lines, and save then exit

check process mysqld with pidfile /var/run/mysqld/mysqld.pid
    start program = "/etc/init.d/mysql start"
    stop program = "/etc/init.d/mysql stop"

Part 4: Verifying and Testing the Configuration

After adding required services in monit monitoring configuration file, Use the below command to verify syntax of file.

# monit -t
Control file syntax OK

Now restart monit service

# service monit restart

Now view the summary of monitoring processes and services by Monit.

# monit summary
The Monit daemon 5.14 uptime: 0m 

Process 'mysqld'      Running
Process 'apache'      Running
System 'SemariLabs00' Running

To view detailed description of each service use the following command

# monit status

[Sample Output]

# monit status
The Monit daemon 5.14 uptime: 0m

Process 'mysqld'
 status Running
 monitoring status Monitored
 pid 1210
 parent pid 1083
 uid 497
 effective uid 497
 gid 498
 uptime 46m 
 children 0
 memory 56.2 MB
 memory total 56.2 MB
 memory percent 5.6%
 memory percent total 5.6%
 cpu percent 0.0%
 cpu percent total 0.0%
 data collected Mon, 17 Oct 2016 12:49:19

Process 'apache'
 status Running
 monitoring status Monitored
 pid 1354
 parent pid 1
 uid 0
 effective uid 0
 gid 0
 uptime 46m 
 children 8
 memory 11.0 MB
 memory total 58.2 MB
 memory percent 1.1%
 memory percent total 5.8%
 cpu percent 0.0%
 cpu percent total 0.0%
 data collected Mon, 17 Oct 2016 12:49:19

System 'SemariLabs00'
 status Running
 monitoring status Monitored
 load average [0.00] [0.00] [0.00]
 cpu 0.0%us 0.0%sy 0.0%wa
 memory usage 128.3 MB [12.9%]
 swap usage 0 B [0.0%]
 data collected Mon, 17 Oct 2016 12:49:19

As you see, we added two services to be monitored with monit and everything is fine

Hints:
1. Take care when adding your own service to populate the service's configuration file with valid locations for pidfile, start program, and stop program.
2. The three needed paths for configuring services is different from a distribution to another.

Summary

In this article, we have explained how to install and configure monit to monitor servers and services. Our installation done on many Linux distributions “CentOS, redhat, Debian, Ubuntu, etc…”. we explained enabling the web interface and the addition of two services to be monitored by monit and if any service crashed, monit will try to bring it up again. Finally, monit can be used to start services at boot time ” I’m using it to start puma ‘application server’ used with ROR at boot time and start it after any crash”.

I hope this article is good enough for you.
See you in other articles.