The main Icinga configuration file is /etc/icinga/icinga.cfg, additional configurations are stored in /etc/icinga/commands.cfg and /etc/icinga/resource.cfg. Usually the default configuration is ok, so you don't have to change these files.
The first thing you should change is the contact details in /etc/icinga/objects/contacts_icinga.cfg so that notifications are sent to the correct email address:
The service checks for localhost (= server1.example.com) are defined in /etc/icinga/objects/localhost_icinga.cfg - take a look at that file:
cat /etc/icinga/objects/localhost_icinga.cfg
# A simple configuration file for monitoring the local host
# This can serve as an example for configuring other servers;
# Custom services specific to this host are added here, but services
# defined in icinga-common_services.cfg may also apply.
#
define host{
use generic-host ; Name of host template to use
host_name localhost
alias localhost
address 127.0.0.1
}
# 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.
define service{
use generic-service ; Name of service template to use
host_name localhost
service_description Disk Space
check_command check_all_disks!20%!10%
}
# Define a service to check the number of currently logged in
# users on the local machine. Warning if > 20 users, critical
# if > 50 users.
define service{
use generic-service ; Name of service template to use
host_name localhost
service_description Current Users
check_command check_users!20!50
}
# Define a service to check the number of currently running procs
# on the local machine. Warning if > 250 processes, critical if
# > 400 processes.
define service{
use generic-service ; Name of service template to use
host_name localhost
service_description Total Processes
check_command check_procs!250!400
}
# Define a service to check the load on the local machine.
define service{
use generic-service ; Name of service template to use
host_name localhost
service_description Current Load
check_command check_load!5.0!4.0!3.0!10.0!6.0!4.0
}
The check_command commands (like check_all_disks) are defined in the Nagios plugin configuration files in the /etc/nagios-plugins/config directory:
As you see, the check_all_disks command is defined as /usr/lib/nagios/plugins/check_disk -w '$ARG1$' -c '$ARG2$' -e. If you take a look at the /etc/icinga/objects/localhost_icinga.cfg file again, you see that we have the line check_command check_all_disks!20%!10% in it. Icinga allows us to pass command line arguments to service checks by separating them with an exclamation mark (!), so check_command check_all_disks!20%!10% means we pass 20% as the first command line argument and 10% as the second command line argument to the /usr/lib/nagios/plugins/check_disk -w '$ARG1$' -c '$ARG2$' -e command so that it finally translates to /usr/lib/nagios/plugins/check_disk -w '20%' -c '10%' -e.
If you want to pass a command line argument that contains an exclamation mark, you must escape the exclamation mark with a backslash: \!
The Nagios plugins (i.e., the tools Icinga uses to run checks) are located in the /usr/lib/nagios/plugins directory:
To find out what command line arguments a plugin can take, call that plugin with the --help switch. For example, to find out how the check_disk plugin can be used, run
/usr/lib/nagios/plugins/check_disk --help
With this knowledge you can modify the service checks in /etc/icinga/objects/localhost_icinga.cfg to your likings, and you can add/modify plugin configurations in the /etc/nagios-plugins/config directory.
Now let's assume we want to add a service check for MySQL, we first take a look at the appropriate plugin configuration:
The command I want to use is check_mysql_cmdlinecred - this takes a MySQL username and a password as arguments (besides the host address which is taken from the host_name parameter of the service check definition. I want to use the MySQL user nagios with the password howtoforge here, so I add the following section to /etc/icinga/objects/localhost_icinga.cfg:
vi /etc/icinga/objects/localhost_icinga.cfg
[...]
define service{
use generic-service
host_name localhost
service_description MySQL
check_command check_mysql_cmdlinecred!nagios!howtoforge
}
Before we restart Icinga, we must create the MySQL user nagios with the password howtoforge:
mysql -u root -p
GRANT USAGE ON *.* TO nagios@localhost IDENTIFIED BY 'howtoforge';
GRANT USAGE ON *.* TO nagios@localhost.localdomain IDENTIFIED BY 'howtoforge';
FLUSH PRIVILEGES;
quit;
(The USAGE privilege is a synonym for 'no privileges', i.e., the nagios user can connect to MySQL, but not alter or read any data.)
Now we restart Icinga so that our changes take effect:
/etc/init.d/icinga restart
If you check localhost's services in the Icinga web interface now, you should see that a check for MySQL has been added:
Likewise, we can add checks for SMTP, POP3, and IMAP - these are just connection checks, so we don't need any arguments:
... and a few moments later you should see the new checks in the Icinga web interface:
You might have noticed the SSH and HTTP checks for localhost which are not defined in /etc/icinga/objects/localhost_icinga.cfg. These are defined in hostgroups in the /etc/icinga/objects/hostgroups_icinga.cfg file. A hostgroup allows us to run a service check for multiple servers and define it only once. Take a look at that file:
cat /etc/icinga/objects/hostgroups_icinga.cfg
# Some generic hostgroup definitions
# A simple wildcard hostgroup
define hostgroup {
hostgroup_name all
alias All Servers
members *
}
# A list of your Debian GNU/Linux servers
define hostgroup {
hostgroup_name debian-servers
alias Debian GNU/Linux Servers
members localhost
}
# A list of your web servers
define hostgroup {
hostgroup_name http-servers
alias HTTP servers
members localhost
}
# A list of your ssh-accessible servers
define hostgroup {
hostgroup_name ssh-servers
alias SSH servers
members localhost
}
As you see, we have a hostgroup called http-servers and a hostgroup called ssh-servers, and localhost is a member of each of these groups. The service checks for the hostgroups are defined in /etc/icinga/objects/services_icinga.cfg. This file contains service checks and refers to the hostgroups to which these checks should be applied by using the hostgroup_name parameter:
cat /etc/icinga/objects/services_icinga.cfg
# check that web services are running
define service {
hostgroup_name http-servers
service_description HTTP
check_command check_http
use generic-service
notification_interval 0 ; set > 0 if you want to be renotified
}
# check that ssh services are running
define service {
hostgroup_name ssh-servers
service_description SSH
check_command check_ssh
use generic-service
notification_interval 0 ; set > 0 if you want to be renotified
}
As you see, the SSH and HTTP service checks are defined here.
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