<s>
Nagios	B-Application
Core	I-Application
,	O
formerly	O
known	O
as	O
Nagios	B-Application
,	O
is	O
a	O
free	B-Application
and	O
open-source	B-Application
computer-software	O
application	O
that	O
monitors	O
systems	B-Application
,	O
networks	O
and	O
infrastructure	O
.	O
</s>
<s>
Nagios	B-Application
offers	O
monitoring	O
and	O
alerting	O
services	O
for	O
servers	O
,	O
switches	O
,	O
applications	O
and	O
services	O
.	O
</s>
<s>
Ethan	O
Galstad	O
and	O
a	O
group	O
of	O
developers	B-Application
originally	O
wrote	O
Nagios	B-Application
as	O
NetSaint	B-Application
.	O
</s>
<s>
they	O
actively	O
maintain	O
both	O
the	O
official	O
and	O
unofficial	O
plugins	B-Application
.	O
</s>
<s>
Nagios	B-Application
is	O
a	O
recursive	O
acronym	O
:	O
"	O
Nagios	B-Application
Ai	O
n't	O
Gonna	O
Insist	O
On	O
Sainthood	O
"	O
–	O
"	O
sainthood	O
"	O
makes	O
reference	O
to	O
the	O
original	O
name	O
NetSaint	B-Application
,	O
which	O
changed	O
in	O
response	O
to	O
a	O
legal	O
challenge	O
by	O
owners	O
of	O
a	O
similar	O
trademark	O
.	O
</s>
<s>
Nagios	B-Application
was	O
originally	O
designed	O
to	O
run	O
under	O
Linux	B-Application
,	O
but	O
it	O
also	O
runs	O
on	O
other	O
Unix	B-Application
variants	O
.	O
</s>
<s>
It	O
is	O
free	B-Application
software	I-Application
licensed	O
under	O
the	O
terms	O
of	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
version	O
2	O
as	O
published	O
by	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
Nagios	B-Application
Remote	O
Plugin	B-Application
Executor	O
(	O
NRPE	O
)	O
is	O
a	O
Nagios	B-Application
agent	O
that	O
allows	O
remote	O
system	B-Application
monitoring	I-Application
using	O
scripts	O
that	O
are	O
hosted	O
on	O
the	O
remote	O
systems	B-Application
.	O
</s>
<s>
Nagios	B-Application
periodically	O
polls	O
the	O
agent	O
on	O
remote	O
system	O
using	O
the	O
check_nrpe	O
plugin	B-Application
.	O
</s>
<s>
NRPE	O
allows	O
you	O
to	O
remotely	O
execute	O
Nagios	B-Application
plugins	B-Application
on	O
other	O
Linux/Unix	O
machines	O
.	O
</s>
<s>
Nagios	B-Application
Remote	O
Data	O
Processor	O
(	O
NRDP	O
)	O
is	O
a	O
Nagios	B-Application
agent	O
with	O
a	O
flexible	O
data	O
transport	O
mechanism	O
and	O
processor	O
.	O
</s>
<s>
NRDP	O
uses	O
standard	O
ports	O
and	O
protocols	O
(	O
HTTP	B-Protocol
and	O
XML	B-Protocol
)	O
and	O
can	O
be	O
implemented	O
as	O
a	O
replacement	O
for	O
Nagios	B-Application
Service	O
Check	O
Acceptor	O
(	O
NSCA	O
)	O
.	O
</s>
<s>
The	O
Nagios	B-Application
plugin	B-Application
that	O
is	O
used	O
to	O
collect	O
information	O
from	O
this	O
addon	O
is	O
called	O
check_nt	O
.	O
</s>
<s>
Nagios	B-Application
is	O
a	O
host	O
and	O
service	O
monitor	O
which	O
is	O
designed	O
to	O
inform	O
you	O
of	O
network	O
problems	O
.	O
</s>
<s>
The	O
Nagios	B-Application
Cross	B-Operating_System
Platform	I-Operating_System
Agent	O
is	O
an	O
open	B-Application
source	I-Application
project	O
maintained	O
by	O
Nagios	B-Application
Enterprises	O
.	O
</s>
<s>
NCPA	O
installs	O
on	O
Windows	O
,	O
Linux	B-Application
,	O
and	O
Mac	O
OS	O
X	O
.	O
</s>
<s>
Created	O
as	O
a	O
scale-able	O
API	B-Application
that	O
allows	O
flexibility	O
and	O
simplicity	O
in	O
monitoring	O
hosts	O
.	O
</s>
<s>
Active	O
checks	O
are	O
queried	O
through	O
the	O
API	B-Application
of	O
the	O
"	O
NCPA	O
Listener	O
"	O
service	O
while	O
passive	O
checks	O
are	O
sent	O
via	O
the	O
"	O
NCPA	O
Passive	O
"	O
service	O
.	O
</s>
<s>
Nagios	B-Application
XI	I-Application
is	O
a	O
proprietary	O
interface	O
using	O
Nagios	B-Application
Core	I-Application
as	O
the	O
back-end	O
,	O
written	O
and	O
maintained	O
by	O
the	O
original	O
author	O
,	O
Ethan	O
Galstad	O
,	O
and	O
Nagios	B-Application
Enterprises	O
.	O
</s>
<s>
CentOS	O
and	O
RHEL	O
are	O
the	O
currently	O
supported	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
It	O
combines	O
Nagios	B-Application
Core	I-Application
with	O
other	O
technologies	O
.	O
</s>
<s>
Its	O
main	O
database	O
and	O
the	O
ndoutils	O
module	O
that	O
is	O
used	O
alongside	O
Nagios	B-Application
Core	I-Application
use	O
MySQL	B-Application
.	O
</s>
<s>
While	O
the	O
front-end	O
of	O
Nagios	B-Application
Core	I-Application
is	O
mainly	O
CGI	B-Language
with	O
some	O
PHP	O
,	O
most	O
of	O
the	O
Nagios	B-Application
XI	I-Application
front-end	O
and	O
back-end	O
are	O
written	O
in	O
PHP	O
including	O
the	O
subsystem	O
,	O
event	O
handlers	O
,	O
and	O
notifications	O
,	O
and	O
Python	B-Language
is	O
used	O
to	O
create	O
capacity	O
planning	O
reports	O
and	O
other	O
reports	O
.	O
</s>
<s>
RRDtool	B-Language
and	O
Highcharts	B-Application
are	O
included	O
to	O
create	O
customizable	O
graphs	O
that	O
can	O
be	O
displayed	O
in	O
dashboards	B-Protocol
.	O
</s>
<s>
On	O
16	O
January	O
2014	O
,	O
Nagios	B-Application
Enterprises	O
redirected	O
the	O
nagios-plugins.org	O
domain	O
to	O
a	O
web	O
server	O
controlled	O
by	O
Nagios	B-Application
Enterprises	O
without	O
explicitly	O
notifying	O
the	O
Nagios	B-Application
Plugins	B-Application
community	O
team	O
the	O
consequences	O
of	O
their	O
actions	O
.	O
</s>
<s>
Nagios	B-Application
Enterprises	O
replaced	O
the	O
nagios-plugins	O
team	O
with	O
a	O
group	O
of	O
new	O
,	O
different	O
members	O
.	O
</s>
<s>
The	O
community	O
team	O
members	O
who	O
were	O
replaced	O
continued	O
their	O
work	O
under	O
the	O
name	O
Monitoring	O
Plugins	B-Application
along	O
with	O
a	O
new	O
website	O
with	O
the	O
new	O
domain	O
of	O
monitoring-plugins.org	O
.	O
</s>
