misc software development snippets

Nagios/nrpe how to (mini version):

For this session, I am demonstrating a basic Nagios set up of nrpe.

There are two hosts involved.
1. the nagios host. (the master node; where the nagios web ui is)
2. the remote host (the node you want to monitor remotely from the master node)

Software Versions involved:
both hosts: CentOS release 5.3 (Final) (64 bit)

master node:
Nagios® Core™ Version 3.2.0
nagios.x86_64 3.2.0-1.el5.rf (yum install)

remote host:
nagios-nrpe.x86_64 2.12-1.el5.rf (yum install)

(I assume you have a basic nagios set up already - this is just to enable nrpe)

nagios host: (master)

$ sudo yum install nagios-plugins-nrpe  nrpe
$ sudo chown nagios.nagios /etc/nagios/nrpe.cfg
$ sudo vi  /etc/nagios/objects/commands.cfg
# add
define command{
        command_name    check_nrpe
        command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}

$ sudo vi /etc/nagios/objects/myremote_host.cfg
# add
define service{
        use                                      remote-service
        host_name                          example.com
        service_description             Check Remote Users
        check_command                  check_nrpe!check_users
}
# nrpe (remote checks) syntax is check_nrpe(as defined above) ! 'command to
 run' (as defined on remote host, see below)

remote host: (node to be remotely monitored)
(NOTE: nagios itself should not be installed on this host)

$ sudo yum install nagios-nrpe
$ cd /etc/nagios
$ sudo chown nagios.nagios *.cfg
$ sudo vim /etc/xinetd.d/nrpe
# add
service nrpe
{
        flags           = REUSE
        type            = UNLISTED
        port            = 5666
        socket_type     = stream
        wait            = no
        user            = nagios
        group           = nagios
        server          = /usr/sbin/nrpe
        server_args     = -c /etc/nagios/nrpe.cfg --inetd
        log_on_failure  += USERID
        disable         = no    # was yes
        only_from       = NAGIOS_MASTER_IP (master nagios host you want to
connect from) # was localhost
}
$ sudo vim cat /etc/hosts.allow
# add same ip from xinetd above
NAGIOS_MASTER_IP

$ sudo vim  /etc/nagios/nrpe.cfg
#allowed_hosts=127.0.0.1   #
# add same ip from xinetd above
allowed_hosts=NAGIOS_MASTER_IP    

$ sudo vim /etc/services
# append this line to the file
# Local services
nrpe            5666/tcp                        # nrpe (nagios)

$ sudo /sbin/service nrpe start
Starting Nagios NRPE daemon (nrpe):                        [  OK  ]
$ sudo /etc/init.d/xinetd reload
$ sudo /sbin/chkconfig --list |grep nrpe
nrpe           	0:off	1:off	2:off	3:off	4:off	5:off	6:off
	nrpe:          	off
$ sudo /sbin/chkconfig --levels 35 nrpe on
$ sudo /sbin/chkconfig --list |grep nrpe
nrpe           	0:off	1:off	2:off	3:on	4:off	5:on	6:off
	nrpe:          	off

$ netstat -an | grep 5666
tcp        0      0 0.0.0.0:5666    0.0.0.0:*    LISTEN

ok, good, it's running

now from nagios (master) server:
(can we see it's running too?)
telnet REMOTE_HOST_WE_JUST_CONFIGURED_IP 5666

$ /usr/lib64/nagios/plugins/check_nrpe -H REMOTE_HOST_WE_JUST_CONFIGURED_IP -p5666 -c check_disk1

to add new commands to be run via nrpe, we must add those to the remote host, nrpe.cfg file:

added new test on remote host:
$ sudo vim /etc/nagios/nrpe.cfg
command[check_mapper]=/usr/lib64/nagios/plugins/check_disk -w 20% -c 10% -p /dev/sda5

test from master node:
$ /usr/lib64/nagios/plugins/check_nrpe -H REMOTE_HOST_WE_JUST_CONFIGURED_IP -p5666 -c check_mapper
DISK OK - free space: / 41180 MB (50% inode=99%);| /=40614MB;68993;77617;0;86242

helpful master node commands:
server config test:
$ sudo /usr/bin/nagios -v /etc/nagios/nagios.cfg
#start/stop/restart:
$ sudo /sbin/service nagios restart
#command line check commands against remote host:
$ /usr/lib64/nagios/plugins/check_nrpe -H REMOTE_SERVER_IP -p5666 -c check_disk1

ref:
http://www.crucialwebhost.com/blog/nagios-howto-using-nrpe-to-monitor-remote-services/
http://ubuntuforums.org/archive/index.php/t-498435.html - bottom comment