= Nagios =
Nagios is a powerful monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes.

== Check nagios configuration ==
{{{#!highlisht bash
/usr/local/nagios/bin/nagios -v  /usr/local/nagios/etc/nagios.cfg
# status service on CentOS
service nagios status
# restart service on CentOS
service nagios restart
}}}

== Install nagios client NRPE on CentOS 6.X ==
 * cd /tmp
 * wget dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
 * rpm -ivh epel-release-6-8.noarch.rpm
 * yum install -y nrpe nagios-plugins-all openssl
 * cp /etc/nagios/nrpe.cfg /etc/nagios/nrpe.cfg.back
 * Edit /etc/nagios/nrpe.cfg and add to allowed_hosts the IP address of the Nagios server
 * service nrpe status
 * service nrpe start
 * chkconfog nrpe on

== Sample service config ==
{{{#!highlisht bash
define service{
    use generic-service
    service_description Secure shell
    check_command check_ssh
}

define service{
    use generic-service
    service_description Web server
    check_command check_http
}

define service{
    use generic-service
    service_description RDP Windows
    check_command check_tcp!3389
}
}}}

== Check command ==
{{{#!highlight bash
/usr/local/nagios/libexec/check_nrpe -H 192.168.1.1 -c check_metric
}}}

== Check http with hostname, url and content ==
Plugin description: https://www.nagios-plugins.org/doc/man/check_http.html 
Search for commands.cfg and define a new command to handle the hostname string and url.

{{{
define command{
  command_name    check_http_content
  command_line    $USER1$/check_http  -w 5 -c 10 -H $ARG1$ -s "$ARG2$" -u $ARG3$
}

define service{
  use generic-service
  host_name SERVERXYZ
  service_description HTTP www.example.net/urlx/
  check_command check_http_content!www.example.net!strInHtml!/urlx/
}

}}}

 * check_http -w 5 -c 10 -H hostname -s "string" -u /urlx/
{{{
./check_http -w 5 -c 10 -H www.sapo.pt  -s "teste" -u /
HTTP OK: HTTP/1.1 200 OK - 391565 bytes in 0.376 second response time |time=0.376469s;5.000000;10.000000;0.000000 size=391565B;;;0

./check_http -w 5 -c 10 -H www.sapo.pt  -s "testesss" -u /
HTTP CRITICAL: HTTP/1.1 200 OK - string not found - 391720 bytes in 0.386 second response time |time=0.385639s;5.000000;10.000000;0.000000 size=391720B;;;0
}}}



== Sample /etc/nagios/nrpe.cfg config file on CentOS 6.3 64 bit, host checked by Nagios ==
{{{
log_facility=daemon
pid_file=/var/run/nrpe/nrpe.pid
server_port=5666
nrpe_user=nrpe
nrpe_group=nrpe
#nagios server 192.168.1.2
allowed_hosts=196.168.1.2,127.0.0.1
dont_blame_nrpe=0
debug=1
command_timeout=60
connection_timeout=300
include_dir=/etc/nrpe.d/

command[check_users]=/usr/lib64/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib64/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_hda1]=/usr/lib64/nagios/plugins/check_disk -w 20% -c 10% -p /dev/hda1
command[check_zombie_procs]=/usr/lib64/nagios/plugins/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/lib64/nagios/plugins/check_procs -w 150 -c 200 
}}}

== check_oracle_health shows warning when OK ==
[[http://forums.meulie.net/viewtopic.php?f=62&t=6282]]

== Nagios shows Warning when is OK ==
Run the command locally on the target server with the user nrpe. Give permission to login to the user.
 * su nrpe
 * mycommand.py
 * echo $?

If there are problems of permissions or similar when running with the user nrpe, solve them testing the commands under the user nrpe.

If the command creates or uses files, delete them if the command tested with root, so they are created properly with the right permissions.

== NRPE: Unable to read output (CentOS 6.3) ==
Make sure the following is setted:
 * setenforce 0
 * nano /etc/sysconfig/selinux # change to SELINUX=disabled

== Change number processes on check_total_procs command ==
If we are getting too many warning mesages regardig the total number of processes do the following:
 * ps uax | wc -l # count the number of active processes on the machine, nrProcs
 * Edit the file /etc/nagios/nrpe.cfg
 * Change command[check_total_procs] setting the warning -w to nrProcs + 20 and -c to nrProcs+20+30
 * Save the file
 * service nrpe restart