Monit is a free, open-source process supervision tool for Unix and Linux. With Monit, system status can be viewed directly from the command line, or via the native HTTP web server. Monit is able to do automatic maintenance, repair, and run meaningful causal actions in error situations.
In this guide we will learn how to install and configure monit on a Rocky Linux 8 server. If you are interested in setting up M/Monit, checkout How to install and set up M/Monit in Linux.
These are some of the features of Monit.
Proactive
Monit can act if an error situation should occur, e.g.; if sendmail is not running, Monit can start sendmail again automatically or if apache is using too much resources (e.g. if a DoS attack is in progress) Monit can stop or restart apache and send you an alert message. Monit can also monitor process characteristics, such as; how much memory or cpu cycles a process is using.
Processes
You can use Monit to monitor daemon processes or similar programs running on localhost. Monit is particularly useful for monitoring daemon processes, such as those started at system boot time from /etc/init/ For instance sendmail, sshd, apache and mysql.
Files, Dirs and Filesystems
You can also use Monit to monitor files, directories and filesystems on localhost. Monit can monitor these items for changes, such as timestamps changes, checksum changes or size changes. This is also useful for security reasons – you can monitor the md5 or sha1 checksum of files that should not change and get an alert or perform an action if they should change.
Cloud and Hosts
Monitor network connections to various servers, either on localhost or on remote hosts. TCP, UDP and Unix Domain Sockets are supported. Network tests can be performed on a protocol level; Monit has built-in tests for the main Internet protocols, such as HTTP, SMTP etc. Even if a protocol is not supported you can still test the server as you can configure Monit to send any data and test the response from the server.
Programs and scripts
Monit can be used to test programs or scripts at certain times, much like cron, but in addition, you can test the exit value of a program and perform an action or send an alert if the exit value indicates an error. This means that you can use Monit to perform any type of check you can write a script for.
System
Finally, Monit can be used to monitor general system resources on localhost such as overall CPU usage, Memory and Load Average.
Step 1: Installing Monit
Monit is available in the default Rocky Linux repositories. Use this command to install?
sudo dnf install -y monitIf you want to install the latest version, use the downloads page here.
Step 2: Starting and enabling service
Once installed, we need to start the monit service. Use this command to start:
sudo systemctl start monitCheck the status to confirm that the service is running using this command:
$ sudo systemctl status monit
● monit.service - Pro-active monitoring utility for unix systems
Loaded: loaded (/usr/lib/systemd/system/monit.service; disabled; vendor preset: disabled)
Active: active (running) since Thu 2022-03-31 15:37:35 UTC; 6s ago
Docs: man:monit(1)
https://mmonit.com/wiki/Monit/HowTo
Main PID: 251683 (monit)
Tasks: 2 (limit: 23465)
Memory: 2.1M
CGroup: /system.slice/monit.service
└─251683 /usr/bin/monit -I
Mar 31 15:37:35 monitoring systemd[1]: Started Pro-active monitoring utility for unix systems.Finally, enable monit on boot:
sudo systemctl enable monitStep 3: Configuring monit service
Enable monit web interface
Monit comes with user friendly-web interface to view the system status and manage them through the web browser. By default, Monit web interface is disabled. You can enable it by editing /etc/monit/monitrc configuration file:
sudo vim /etc/monitrcMake the following changes. The allow directive will require user ‘admin’ with password ‘monit’ for the web login.
set httpd port 2812
allow admin:monitSet up M/Monit host
M/monit provides a central view of all mmonit data. It is helpful when you are managing muliple servers and do not want to login to each of them to check the status. The format of the url is http://[username]:[password]@[host]:[port]/collector.
Use this command in monitrc to configure mmonit host:
set mmonit http://monit:monit@10.2.11.10:8080/collectorFinal monit configuration
set daemon 30
set log syslog
set idfile /var/.monit.id
set statefile /var/.monit.state
set eventqueue
basedir /var/lib/monit/events
slots 100
set httpd port 2812 and
use address 10.2.11.10 #only accept connection from localhost
allow 0.0.0.0/0.0.0.0
allow admin:monit
set mmonit http://monit:monit@10.2.11.10:8080/collector
include /etc/monit.d/*Restart mmonit to apply changes
Save the file, then restart Monit service to apply the changes:
sudo systemctl restart monitStep 4: Allow service through firewall
If you have firewalld installed and enabled, use this command to whielist monit port for external access.
sudo firewall-cmd --permanent --add-port=2812/tcp
sudo firewall-cmd --reloadStep 5: Accessing the web interface
Open your web browser and type the URL http://[your_servr_ip]:2812. You will be redirected to the Monit login page. Provide monit username as admin and password as monit, then click on the Sign In button. You should see the Monit default dashboard.
Step 6: Configure monit for a service with pid
The line include /etc/monit.d/* in the file /etc/monitrc includes all defined configurations in monit.d directory. It is recommended to include individual configurations there.
We will use grafana-server as a example. We will need to create the configuration file for grafana-server. You can do this with the following command:
sudo vim /etc/monit.d/grafana-serverThen add this content:
check process grafana-server with pidfile /var/run/grafana/grafana-server.pid
start program = "/bin/systemctl start grafana-server" with timeout 15 seconds
stop program = "/bin/systemctl stop grafana-server"
if failed port 3000 protocol http then restartNext, verify the Monit status with the following command:
monit -tOutput:
$ sudo monit -t
Control file syntax OKAfter resolving any possible syntax errors, you can start running all of the monitored programs.
monit start all
Next, restart the Monit service to apply the changes:
sudo systemctl reload monitYou can see the new service on the Monit web interface. Or you can use the status command in the terminal:
$ sudo monit status
Monit 5.30.0 uptime: 12h 18m
Process 'grafana-server'
status OK
monitoring status Monitored
monitoring mode active
on reboot start
pid 43609
parent pid 1
uid 989
effective uid 989
gid 986
uptime 22d 11h 11m
threads 11
children 0
cpu 0.0%
cpu total 0.0%
memory 2.7% [102.2 MB]
memory total 2.7% [102.2 MB]
security attribute system_u:system_r:unconfined_service_t:s0
filedescriptors 13 [0.1% of 10000 limit]
total filedescriptors 13
read bytes 216.2 B/s [770.4 MB total]
disk read bytes 0 B/s [2.3 MB total]
disk read operations 2.1 reads/s [4070127 reads total]
write bytes 24.8 B/s [331.1 MB total]
disk write bytes 136.5 B/s [167.5 MB total]
disk write operations 1.8 writes/s [3258928 writes total]
port response time 1.485 ms to localhost:3000 type TCP/IP protocol HTTP
data collected Fri, 01 Apr 2022 03:57:26
System 'monitoring'
status OK
monitoring status Monitored
monitoring mode active
on reboot start
load average [0.04] [0.02] [0.00]
cpu 1.1%usr 0.6%sys 0.0%nice 0.0%iowait 0.2%hardirq 0.1%softirq 0.1%steal 0.0%guest 0.0%guestnice
memory usage 1.1 GB [31.1%]
swap usage 0 B [0.0%]
uptime 22d 13h 10m
boot time Wed, 09 Mar 2022 14:47:17
filedescriptors 2496 [0.7% of 374156 limit]
data collected Fri, 01 Apr 2022 03:57:26Step 7: Monitor local system
We can also use monit to monitor and alert on local system resource usage. This file monitors for load average, memory, swap and cpu usage and alerts on thresholds defined.
check system $HOST
if loadavg (1min) > 10 then alert
if loadavg (5min) > 2 then alert
if memory usage > 75% then alert
if swap usage > 25% then alert
if cpu usage (user) > 70% then alert
if cpu usage (system) > 30% then alert
if cpu usage (wait) > 20% then alertConclusion
Congratulations! You have successfully installed Monit monitoring tool on your rocky linux server.