Info Tech Articles

Nagios Installation and Configuration

Getting Nagios

You need root access on the server, where you would like to install Nagios. Login as root.

Create a directory for downloads.

#mkdir -p /usr/src/backs/nagios
#cd /usr/src/backs/nagios

Download source of nagios and nagios-plugins at http://www.nagios.org/download/.

#wget http://keihanna.dl.sourceforge.net/sourceforge
/nagios/nagios-1.2.tar.gz

#wget http://easynews.dl.sourceforge.net/sourceforge
/nagiosplug/nagios-plugins-1.3.1.tar.gz

Compilation and installation of Nagios

#su
#adduser nagios
#passwd nagios
Changing password for user nagios.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.

In some servers normal users may not have permission to use ‘mail’ inorder to send alerts.

usermod -G mail nagios

Make a directory for working with the source code.

mkdir -p /usr/src/works/nagios
cd /usr/src/works/nagios/
tar -zxvf /usr/src/backs/nagios/nagios-1.2.tar.gz
cd nagios-1.2/
 ./configure

The default is fine for normal operation.
for details see the file 'INSTALL'.

./configure --prefix=prefix --with-cgiurl=cgiurl
--with-htmurl=htmurl --with-nagios-user=someuser
--with-nagios-grp=somegroup

./configure
make all
make install
make install-init # Needed to add the service 'nagios'.
make install-commandmode
make install-config

Install the plugins

cd ../
tar -zxvf /usr/src/backs/nagios/nagios-plugins-1.3.1.tar.gz
cd nagios-plugins-1.3.1/
./configure

NOTE:- For mysql and postgresql plugins to work,
their  libraries have to be installed. so to avoid
installing those we will use 'check_tcp'
Instead later with seperate port for mysql and postgresql.

make
make check
make install

Libraries will be installed in ‘/usr/local/nagios/libexec’ position by the default installation.
If there is no contents do the following.

 mkdir /usr/local/nagios/libexec
 mv /usr/lib/nagios/plugins/* /usr/local/nagios/libexec/
 ln -s /lib/libcrypto.so.0.9.7a /lib/libcrypto.so.4

Post install Configuration of Nagios

Edit apache’s httpd.conf file. (the location of the httpd.conf file may differ)

vim /etc/httpd/conf/httpd.conf

Add the following line at the end of the file.

Include /etc/httpd/conf/nagios.conf

Create the file ‘/etc/httpd/conf/nagios.conf’.

vi /etc/httpd/conf/nagios.conf

Add the following contents to this file.
————————————————-
ScriptAlias /nagios/cgi-bin/ /usr/local/nagios/sbin/

AllowOverride AuthConfig
Options ExecCGI
Allow from all
Order allow,deny

Alias /nagios/ /usr/local/nagios/share/

Options None
AllowOverride AuthConfig
Order allow,deny
Allow from all
————————————————–

Make sure the updations done with http is fine and restart apache.

#service httpd restart

Create ‘.htaccess’ file in ‘/usr/local/nagios/share/’ and ‘/usr/local/nagios/sbin/’.

#touch /usr/local/nagios/share/.htaccess
#touch /usr/local/nagios/sbin/.htaccess

Add the following contents to both these files.

AuthName "Nagios Access"
AuthType Basic
AuthUserFile /usr/local/nagios/etc/htpasswd.users
require valid-user

Create the username, password for logging into the Nagios interface.

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
ls -l /usr/local/nagios/etc/htpasswd.users

Make it available for the user who runs httpd.

chmod o+r /usr/local/nagios/etc/htpasswd.users

Restart the httpd service.

service httpd restart

Advanced Nagios Configurations.

Rename the sample files to the real names.

cd /usr/local/nagios/etc/
for i in *sample ; do mv $i `echo "$i" |sed s/-sample//` ; done

Edit the main conf file, nagios.cfg. and change only these lines.

check_external_commands=1

Make these Cgi specific changes in cgi.cfg.

use_authentication=1
authorized_for_system_information=nagiosadmin
authorized_for_configuration_information=nagiosadmin
authorized_for_system_commands=nagiosadmin
authorized_for_all_services=nagiosadmin
authorized_for_all_hosts=nagiosadmin
authorized_for_all_service_commands=nagiosadmin
authorized_for_all_host_commands=nagiosadmin

Add servers that need to be monitored

Make the Host specific changes to the hosts.cfg.

 Generic host definition template
define host{
        name                            generic-host
        notifications_enabled          1
        event_handler_enabled          1
        flap_detection_enabled          1
        process_perf_data              1
        retain_status_information      1
        retain_nonstatus_information    1

        register                        0
        }

define host{
        use                    generic-host            ; Name of host
template to use

        host_name              
        alias                  
        address                
        check_command          check-host-alive
        max_check_attempts      10
        notification_interval  120
        notification_period    24x7
        notification_options    d,u,r
        }

Repeat for all the hosts we want to check.
Group them in hostgroups.cfg

define hostgroup{
        hostgroup_name  
        alias          
        contact_groups  
        members        <,,..>
}

Repeat for all the hosts groups.

Specify the services that need to be checked

Edit the details of all the services, we want checked by Nagios in services.cfg.

 Generic service definition template
define service{
        name                            generic-service
        active_checks_enabled          1
        passive_checks_enabled          1
        parallelize_check              1
        obsess_over_service            1
        check_freshness                0
        notifications_enabled          1
        event_handler_enabled          1
        flap_detection_enabled          1
        process_perf_data              1
        retain_status_information      1
        retain_nonstatus_information    1
        register                        0
        }

define service{
        use                            generic-service
        host_name                      
        service_description            
        is_volatile                    0
        check_period                    24x7
        max_check_attempts              3
        normal_check_interval          3
        retry_check_interval            1
        contact_groups                  
to send>
        notification_interval          120
        notification_period            24x7
        notification_options            w,u,c,r
        check_command                  
        }

Repeat for each service on each host.

Specify Alert Contacts

In order to specify details of the contacts for alerts, we need to edit contacts.cfg.

 'nagios' contact definition
define contact{
        contact_name                    
        alias                          
        service_notification_period    24x7
        host_notification_period        24x7
        service_notification_options    w,u,c,r
        host_notification_options      d,u,r
        service_notification_commands  notify-by-email,notify-by-epager
        host_notification_commands
host-notify-by-email,host-notify-by-epager
        email                          
        pager                          
        }

Repeat for all contacts.

Group the contacts

Edit contactgroups.cfg, in order to specify groups of contacts.

define contactgroup{
        contactgroup_name      
        alias                  
        members                
        }

Repeat for all groups to include all contacts

Escalation with nagios

If you need to send selective alerts, for example when critical issues occur, simply configure the escalations.cfg file.

define serviceescalation{
        host_name                      
        service_description            < name>
        first_notification              2
        last_notification              6
        contact_groups                  < groups (comma seperated)>
        notification_interval          0
        }

Repeat for all escalations Once again, check all the files, nagios.cfg cgi.cfg hosts.cfg hostgroups.cfg, services.cfg, contacts.cfg, contactgroups.cfg, escalations.cfg and checkcommands.cfg Restart httpd and then Nagios.

service httpd restart

Add Nagios to system services.

chkconfig --add nagios
service nagios restart

Check for any errors reported, and solve them one by one if any.
Enable nagios in runlevels, so that it starts on boot.

chkconfig nagios on

Create cron.daily entry if we want to restart the service daily. Here is the script.

vi etc/cron.daily/nagios-restart.cron
#!/bin/sh
/sbin/service nagios restart >/dev/null 2>&1

Make it executable

chmod +x etc/cron.daily/nagios-restart.cron

And finally, Check if nagios is working fine.!!!

http://NAGIOS-SERVER-NAME/nagios/index.html