How to Install and Configure Monit on Linux for Process Monitoring

Monit is an open source utility that provides several system monitoring functionality that are extremely helpful to sysadmins. This article provides a jumpstart guide on monit installation and configuration. We also discuss a specific example related to processes monitoring.

1. Install monit

On Fedora, openSUSE, Debian install monit as a package from the distribution repository. For example, on Debian (and Ubuntu), install monit using apt-get as shown below.

# apt-get install monit

If your distribution don’t have the monit package, download monit source and install it.

2. Configure monit

A sample process monitoring entry in the monit configuration file /etc/monit/monitrc looks like the following.

check process PROCESSNAME
        with pidfile PIDFILENAME-WITHABSOLUTE-PATH
        start = STARTUP-SCRIPT
        stop = STOP-SCRIPT

For example, to monitor the cron daemon, append the following lines to the monitrc file.

# vim /etc/monit/monitrc
check process crond
            with pidfile /var/run/crond.pid
            start = "/etc/init.d/cron start"
            stop  = "/etc/init.d/cron stop"

For further configurations (for example, restarting a process when it crosses a memory or process limit), refer the HOW TO MONITOR section in “man monit”.

Also, enable syslog by uncommenting the following line in /etc/monit/monitrc.

# vim /etc/monit/monitrc
set logfile syslog facility log_daemon

3. Allow startup of monit

Edit the /etc/default/monit file and enable the start up flag, which ensures that the configuration is done so that monit can start.

# vim /etc/default/monit
startup=1

4. Start monit

# /etc/init.d/monit start
Starting daemon monitor: monit

5. Check monit functionality

To test this, let us kill the running cron daemon as shown below.

# ps -ef | grep cron
root      2886     1  0 10:18 ?        00:00:00 /usr/sbin/cron

# pkill -9 cron

In the next interval, monit automatically starts the cron daemon without the administrator interaction as shown in the syslog messages below.

Dec  5 13:06:55 (none) monit[2968]: 'crond' process is not running
Dec  5 13:06:55 (none) monit[2968]: 'crond' trying to restart
Dec  5 13:06:55 (none) monit[2968]: 'crond' start: /etc/init.d/cron

Do a ps -ef to make sure the cron job is started automatically by monit, when you killed it.

# ps -ef | grep cron
root     19728     1  0 13:06 ?        00:00:00 /usr/sbin/cron

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