About Monit
Monit is a free, open source process supervision tool for Linux like operating systems. With Monit, system status can be viewed directly from the command line, or via the web browser. Monit is able to do automatic maintenance, repair, and run meaningful causal actions in error situations.
Install Monit
yum -y install monit
Start monit by using the following command.
monit
Check the monit status.
monit status
The output will be as below:
Once monit is installed, you can add programs and processes to the configuration file.
The main configuration file is /etc/monitrc
vi /etc/monitrc
By default, monit is set to check the services at an interval of 1 min. This can be altered as per your need by changing the below line.
set daemon 60
Change log file by editing the following line:
set logfile syslog
Set up monit web interface
Monit provides a web interface for process monitoring. By default, monit listens on 2812 port, but it needs to be set up.
Open monit configuration file /etc/monitrc.
vi /etc/monitrc
Look for httpd port 2812, modify the following entries.
FROM:
set httpd port 2812 and
use address localhost # only accept connection from localhost
allow localhost # allow localhost to connect to the server and
allow admin:monit # require user ‘admin’ with password ‘monit’
allow @monit # allow users of group ‘monit’ to connect (rw)
allow @users readonly # allow users of group ‘users’ to connect readonly
TO:
set httpd port 2812
allow 0.0.0.0/0.0.0.0
allow localhost
allow admin:monit
From the settings, monit will listen on 2812; admin user with password monit will able to access the web interface from any network.
Restart monit.
systemctl restart monit
Auto-start Monit on start-up.
systemctl enable monit
Accessing monit web interface
Open web browser and go to the below address:
http://ip-addr:2812
Use the username and password mentioned before.
Monit home page will look like this:
Configure services for monitoring with monit
To configure the services which we want to monitor with monit we have to add seperate configuration files under the directory /etc/monit.d/ in which default configuration looks for extra configuration files.
Configuration file for HTTP:
vi /etc/monit.d/httpdmonitor
and edit the file as shown below:
check process httpd with pidfile /var/run/httpd/httpd.pid
start program “/usr/bin/systemctl start httpd.service”
stop program “/usr/bin/systemctl stop httpd.service”
if failed port 80 protocol http then restart
Configuration file for ssh:
vi /etc/monit.d/sshdmonitor
and edit the file as shown below:
check sshd with pidfile /var/run/sshd.pid
start program “/usr/bin/systemctl start sshd.service”
stop program “/usr/bin/systemctl stop sshd.service”
if failed port 22 protocol ssh then restart
Configuration file for Mysql:
vi /etc/monit.d/mysql
and edit the file as below:
check process mysqld with pidfile /var/run/mysqld/mysqld.pid
start program = “/etc/init.d/mysql start”
stop program = “/etc/init.d/mysql stop”
if failed port 3306 protocol mysql then restart
Configuration file for Disk monitoring:
vi /etc/monit.d/diskmonitor
and edit the file as below:
check filesystem disk1 with path /dev/xvda1
if SPACE usage > 50% then alert
Here my filesystem is /dev/xvda1. You have to confirm your filesystem before entering the name.
You can do that by using the command:
df -h
The output will be as below:
Configuration file for syslog:
vi /etc/monit.d/syslogmonitor
and edit the file as below:
check process syslogd with pidfile /var/run/syslogd.pid
start program = “/usr/bin/systemctl start rsyslog.service”
stop program = “/usr/bin/systemctl stop rsyslog.service”
Once configured, test the monit syntax
monit -t
ouput of the above command shows:
Control file syntax OK
The above message indicate that all the configuration files are correctly entered.
Reload monit, to take effect of changes:
monit reload
We can see the new services that we configured just now through the web interface.
Mail Alerting with Monit
There are predefined alerting templates available in Monit to alert admins when the particular service fails.
Edit the configuration file.
vi /etc/monitrc
You can update the below alerting template as per your requirement:
set mail-format {
from: monit@$HOST
subject: monit alert — $EVENT $SERVICE
message: $EVENT Service $SERVICE
Date: $DATE
Action: $ACTION
Host: $HOST
Description: $DESCRIPTION
Your faithful employee,
Monit Team
}
Set the recipient address here.
set alert admin@spotfixcrew.com
Use your email-id in place of “admin@spotfixcrew.com”
Note: You will receive alerts on all type of actions
If you do not like to alert on user-initiated service restart, then add the below configuration:
set alert admin@spotfixcrew.com not on { instance, action }
Finally, set the mail server configuration so that you can receive mails:
set mailserver mx.spotfixcrew.com port 25
Reload the service:
monit reload
