CentOS 8
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Nagios 4 : Set Thresholds
2020/01/15
 
This is the Threshold settings section.
It is set on some items by default but if you change it, configure like follows.
[1] The thresholds are set in configuration file by default. For example, the item for monitoring disk usage of root partition is set like follows.
[root@dlp ~]#
vi /etc/nagios/objects/localhost.cfg
.....
.....
# Define a service to check the disk space of the root partition
# on the local machine.  Warning if < 20% free, critical if
# < 10% free space on partition.

# the thresholds are set as Warning if > 20% free, critical if 10% > 10% free

# change these values if you'd like to change them

define service {

    use                     local-service           ; Name of service template to use
    host_name               localhost
    service_description     Root Partition
    check_command           check_local_disk!20%!10%!/
}
.....
.....

[root@dlp ~]#
systemctl restart nagios

[2] For the case you add a new plugin and configure it, set like follows. (example below is for [check_ntp_time] plugin)
[root@dlp ~]#
dnf --enablerepo=epel -y install nagios-plugins-ntp
# display options for a plugin to confirm usage

[root@dlp ~]#
/usr/lib64/nagios/plugins/check_ntp_time -h

.....
.....

 -w, --warning=THRESHOLD
    Offset to result in warning status (seconds)
 -c, --critical=THRESHOLD
    Offset to result in critical status (seconds)

.....
.....

# add definition of command for a plugin with thresholds' options

[root@dlp ~]#
vi /etc/nagios/objects/commands.cfg
# add to the end

define command {
    command_name    check_ntp_time
    command_line    $USER1$/check_ntp_time -H $ARG1$ -w $ARG2$ -c $ARG3$
}

# add definition of service with thresholds' values

[root@dlp ~]#
vi /etc/nagios/objects/localhost.cfg
# add to the end ( Warning with 1 sec time difference, Critical with 2 sec difference )

define service {
    use                     local-service
    host_name               localhost
    service_description     NTP_TIME
    check_command           check_ntp_time!ntp1.jst.mfeed.ad.jp!1!2
    notifications_enabled   1
}

[root@dlp ~]#
systemctl restart nagios

[3] The notification is sent if a system value is over the threshold.
From nagios@dlp.srv.world  Mon Jan 13 23:27:54 2020
Return-Path: <nagios@dlp.srv.world>
X-Original-To: root@localhost
Delivered-To: root@localhost
Date: Mon, 13 Jan 2020 23:27:54 -0600
To: root@localhost
Subject: ** PROBLEM Service Alert: localhost/NTP_TIME is CRITICAL **
User-Agent: Heirloom mailx 12.5 7/5/10
Content-Type: text/plain; charset=us-ascii
From: nagios@dlp.srv.world
Status: R

***** Nagios *****

Notification Type: PROBLEM

Service: NTP_TIME
Host: localhost
Address: 127.0.0.1
State: CRITICAL

Date/Time: Mon Jan 13 23:27:54 CST 2020

Additional Info:

NTP CRITICAL: Offset 65.38857508 secs, stratum best:2 worst:2
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