Install packages

sudo apt-get install nagios3 --no-install-recommends	# use "--no-install-recommends" in order not to install samba packages
sudo apt-get install nagios-images
sudo apt-get install nsca && update-rc.d nsca enable

Make directories for custom configs

sudo mkdir -p /etc/nagios3/custom/{commands,hosts,services,templates}

Edit /etc/nagios3/nagios.cfg

--- nagios.cfg.orig     2012-02-15 21:10:11.000000000 +0400
+++ nagios.cfg  2012-05-17 14:40:43.734332705 +0400
@@ -55,6 +55,10 @@
 #cfg_dir=/etc/nagios3/printers
 #cfg_dir=/etc/nagios3/switches
 #cfg_dir=/etc/nagios3/routers
+cfg_dir=/etc/nagios3/custom/commands
+cfg_dir=/etc/nagios3/custom/hosts
+cfg_dir=/etc/nagios3/custom/services
+cfg_dir=/etc/nagios3/custom/templates
 
 
 
@@ -142,7 +146,8 @@
 # you will have to enable this.
 # Values: 0 = disable commands, 1 = enable commands
 
-check_external_commands=0
+#check_external_commands=0
+check_external_commands=1
 
 
 
@@ -1027,7 +1032,8 @@
 # manner.
 # Values: 1 = enabled freshness checking, 0 = disable freshness checking
 
-check_host_freshness=0
+#check_host_freshness=0
+check_host_freshness=1

Change permissions to /var/lib/nagios3

# Change directory permissions and make the changes permanent in order to make external commands work (check /usr/share/doc/nagios3/README.Debian for more information)
/etc/init.d/nagios3 stop
dpkg-statoverride --update --add nagios www-data 2710 /var/lib/nagios3/rw
dpkg-statoverride --update --add nagios nagios 751 /var/lib/nagios3
/etc/init.d/nagios3 start

Add /etc/nagios3/custom/templates/generic-host-passive.cfg

define host{
        name                            generic-host-passive
        use                             generic-host
        active_checks_enabled           0
        check_freshness                 1
        check_command                   return-unknown
        register                        0
        }

Add /etc/nagios3/custom/templates/generic-service-passive.cfg

define service{
        name                            generic-service-passive
        use                             generic-service
        active_checks_enabled           0
        check_freshness                 1
        check_command                   return-unknown
        register                        0
        }

Create a user and password

# Create htpasswd file and set a password for nagiosadmin (this information is used to access the web-interface)
htpasswd -c /etc/nagios3/htpasswd.users nagiosadmin

Examples of a passive host and a service definitions:

Install packages

sudo apt-get install nagios3-core
sudo apt-get install nagios3-cgi --no-install-recommends	# use "--no-install-recommends" in order not to install apache2 packages
sudo apt-get install nsca

Disable localhost checking in order not to confuse with localhost on the Central Server

sudo rename 's/$/.disabled/' /etc/nagios3/conf.d/{extinfo_nagios2,hostgroups_nagios2,localhost_nagios2,services_nagios2}.cfg

Edit /etc/nagios3/nagios.cfg

--- nagios.cfg.orig	2011-06-07 17:08:33.000000000 +0400
+++ nagios.cfg	2012-05-18 14:57:29.343833057 +0400
@@ -55,6 +55,9 @@
 #cfg_dir=/etc/nagios3/printers
 #cfg_dir=/etc/nagios3/switches
 #cfg_dir=/etc/nagios3/routers
+cfg_dir=/etc/nagios3/commands
+cfg_dir=/etc/nagios3/hosts
+cfg_dir=/etc/nagios3/services
 
 
 
@@ -808,7 +811,8 @@
 # service notifications when it is initially (re)started.
 # Values: 1 = enable notifications, 0 = disable notifications
 
-enable_notifications=1
+#enable_notifications=1
+enable_notifications=0
 
 
 
@@ -913,7 +917,8 @@
 # implementing distributed monitoring.
 # Values: 1 = obsess over services, 0 = do not obsess (default)
 
-obsess_over_services=0
+#obsess_over_services=0
+obsess_over_services=1
 
 
 
@@ -926,6 +931,7 @@
 # more information on implementing distributed monitoring.
 
 #ocsp_command=somecommand
+ocsp_command=submit_check_result_via_nsca_service
 
 
 
@@ -937,7 +943,8 @@
 # implementing distributed monitoring.
 # Values: 1 = obsess over hosts, 0 = do not obsess (default)
 
-obsess_over_hosts=0
+#obsess_over_hosts=0
+obsess_over_hosts=1
 
 
 
@@ -950,6 +957,7 @@
 # more information on implementing distributed monitoring.
 
 #ochp_command=somecommand
+ochp_command=submit_check_result_via_nsca_host
 
 
 

Edit /etc/nagios3/resource.cfg

--- resource.cfg.orig	2011-06-07 17:07:47.000000000 +0400
+++ resource.cfg	2012-05-12 17:39:46.125679961 +0400
@@ -24,7 +24,7 @@
 $USER1$=/usr/lib/nagios/plugins
 
 # Sets $USER2$ to be the path to event handlers
-#$USER2$=/usr/lib/nagios/plugins/eventhandlers
+$USER2$=/usr/share/nagios3/plugins/eventhandlers
 
 # Store some usernames and passwords (hidden from the CGIs)
 #$USER3$=someuser

Add /etc/nagios3/commands/submit_check_result_via_nsca_host.cfg

define command{
        command_name    submit_check_result_via_nsca_host
        command_line    $USER2$/distributed-monitoring/submit_check_result_via_nsca $HOSTNAME$ $HOSTSTATEID$ '$HOSTOUTPUT$|$HOSTPERFDATA$'
}

Add /etc/nagios3/commands/submit_check_result_via_nsca_service.cfg

define command{
        command_name    submit_check_result_via_nsca_service
        command_line    $USER2$/distributed-monitoring/submit_check_result_via_nsca $HOSTNAME$ '$SERVICEDESC$' $SERVICESTATEID$ '$SERVICEOUTPUT$|$SERVICEPERFDATA$'
}

Examples of an active host and a service definitions: