INSTALLATION

Installation takes just a few easy steps. As I installed it on Debian box so used apt-get for installation:
apt-get install nagios3

After nagios was installed I created new monitoring user root with password root123 to have access to web page:
htpasswd -cb /etc/nagios3/htpasswd.users root root123

And start new service:
/etc/init.d/nagios3 start

SETTING UP

All Almost all configuration are stored at /etc/nagios3/conf.d.

I have one administrator and one contact group of course. So I remained example configuration and change only my mail address at contacts_nagios2.cfg:
email my@address.com

I’m gonna monitoring 3 linux hosts plus one router with next services:
1. Master

• dns
• httpd
• http + ssl
• samba
• nis
• ftp
• openvpn  ( don’t have corresponding script. Probably make my own.)
• ping
• smtp
• imap
• mysql
• ssh
• processes
• disk usage
• swap utilization
• users
• uptime
• current load

2. Slave

• processes
• swap
• disk usage
• users
• http
• ssh
• current load
• ping
• uptime

3. Test

• ldap ( was unable  to configure script check through  the tcp_check)
• ping
• ssh
• samba

4. Router

• ping

First of all you need to define all hosts in localhost_nagios2.cfg:
define host{
use generic-host ; Name of host template to use
host_name secondary
alias Secondary
address 192.168.7.177
}

Where, use refers to generic-host in generic-host_nagios2.cfg. I left everything as was:
define host{
name generic-host ; The name of this host template
notifications_enabled 1 ; Host notifications are enabled
event_handler_enabled 1 ; Host event handler is enabled
flap_detection_enabled 1 ; Flap detection is enabled
failure_prediction_enabled 1 ; Failure prediction is enabled
process_perf_data 1 ; Process performance data
retain_status_information 1 ; Retain status information across program restarts
retain_nonstatus_information 1 ; Retain non-status information across program restarts
check_command check-host-alive
max_check_attempts 10
notification_interval 0
notification_period 24x7
notification_options d,u,r
contact_groups admins
register 0 ; DONT REGISTER THIS DEFINITION - ITS NOT A REAL HOST, JUST A TEMPLATE!
}


You can customize it – set group who will be notified in case of emergency and time-frame for notification.

Also you can make some host groups if you want. It’s not necessary but it can simplify service management if you have a lot of hosts. To define host group go to hostgroups_nagios2.cfg:

define hostgroup {
hostgroup_name all
alias All Servers
members *
}define hostgroup {
hostgroup_name debian-servers
alias Debian GNU/Linux Servers
members secondary, master
}

Here we created two groups of hosts: all and debian-servers. All contains all defined hosts in configuration and debian-servers just a secondary and master hosts.

And at the end most interesting and most resource-intensive part – services. For example if you need to monitor HTTP server on host master put next lines in services_nagios2.cfg:

define service {
host_name master
service_description HTTP
check_command check_http
use generic-service
notification_interval 0
}

Next example if you want to just ping router put:
define service {
host_name router
service_description PING
check_command check_ping!100.0,20%!500.0,60%
use generic-service
notification_interval 0
}

If you need sent arguments to monitoring script separate it by ‘!’.
To monitor group of servers use hostgroup_name intead of host_name, like:
hostgroup_name all
- to monitoring all servers described in hostgroup all.

To monitoring such stuff like disk usage, process, users, swap and memory utilization I followed direction from official site.

PROBLEMS

The mail notifications wasn’t work for me. I suggest because there is no mail server on box. I tried to described it in the configuration but haven’t found anything could help me. So I wrote little script to send a mail directly to another smtp server:

#!/usr/bin/perluse strict;
use MIME::Lite;
use Getopt::Long;

Please define variables smtp and to by yourself. And remember that perl modules MIME::Lite and Getopt::Long have to be preinstalled in the system.

And change lines at /etc/nagios3/commands.cfg appropriately:
command_line /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /usr/bin/mail -s "** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **" $CONTACTEMAIL$
and
command_line /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /root/scripts/mail.pl -s "** $NOTIFICATIONTYPE$ Service Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" -t $CONTACTEMAIL$

To those ones:
command_line /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /path/to/mail.pl -s "** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **" -t $CONTACTEMAIL$
and
command_line /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$" | /root/scripts/mail.pl -s "** $NOTIFICATIONTYPE$ Service Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" -t $CONTACTEMAIL$

Where, /root/scripts/mail.pl path to script mail.pl which was provided above.

To make it works you have to install next perl libraries :

Net::SSH::Expect;
Net::SCP::Expect;
Net::SFTP::Foreign;
Net::FTP;

It’s easy to do through cpan. For example:

# cpan i Net::SSH::Expect

or download directly from cpan

function exec_cmd__ :

This function execute command at remote host. Example:

exec_cmd__(hostname, username, password, port, command)

function sub transfer_file__ :

This function can get or put file to remote host via ssh. Example :

transfer_file__(hostname, username, password, port, source file|directory, destination file|directory, method)

where option “method” can be “fh”(means get file from somewhere and put to localhost) or “th”(send file to host)

function sub sftp_func__ :

This function can get and send file to remote computer via sftp protocol. Example
sftp_func__(hostname, username, password, port, source file|directory, destination file|directory, method)

Where option “method” can be ‘get’(get file from remote host) and ‘put’(put file to remote host) and ‘del’(delete file from remote host )
NOTICE: if you use method “del” please specify the target as “source_file” and skip “destination_file” option

function ftp_func__ :

This function get and delete remote file via ftp protocol. Example:

ftp_func__(hostname, username, password, port, source file|directory, destination file|directory, method)
where option “method” can be ‘get’ or ‘put’

function get_file_via_ftp__:

This function is the same to previous one EXCEPT its doesn’t put a file at remote computer and when its get a file doesn’t remove it at remote system. Example:

get_file_via_ftp(hostname, username, password, port, source file|directory, destination file|directory)

function get_yesterday__:

This function return date of yesterday in format which was got by function as first argument. Example:

get_yesterday__(“YYYYDDMM”), get_yesterday__(“DDMMYYYY”) and so on.

How it’s use? Good question :)

Download this library and put into the /usr/lib/perl5/Net/. Ex.:

# cp monitoring.pm /usr/lib/perl5/Net/

Create new test script :
$ cat > test.pl
#!/usr/bin/perl
use monitoring;
$yesterday=monitoring::get_yesterday__("DDMMYYYY");
print "$yesterday\n";


Set executable rights:
$ chmod +x test.pl

And run it:
$ ./test.pl
11062009

That’s all :)