nagios-nrpe/README.md

NRPE

Nagios Remote Plugin Executor

For installation instructions and information on the design overview of the NRPE addon, please read the PDF documentation that is found in this directory: docs/NRPE.pdf.

If you are upgrading from a previous version, you'll want to check the Changelog and then run ./update-cfg.pl to add the new SSL parameters to your config file.

TL;DR: You can jump straight to Compiling and Installing

You'll want to read up on the Security document regarding NRPE, no doubt.

And make sure to check out the SSL Readme as well, if you plan on using encryption methods to transmit nrpe data.

Purpose

The purpose of this addon is to allow you to execute Nagios plugins on a remote host in as transparent a manner as possible.

Contents

There are two pieces to this addon:

1. nrpe

   This program runs as a background process on the remote host and processes command execution requests from the check_nrpe plugin on the Nagios host. Upon receiving a plugin request from an authorized host, it will execute the command line associated with the command name it received and send the program output and return code back to the check_nrpe plugin

2. check_nrpe

   This is a plugin that is run on the Nagios host and is used to contact the NRPE process on remote hosts. The plugin requests that a plugin be executed on the remote host and wait for the NRPE process to execute the plugin and return the result. The plugin then uses the output and return code from the plugin execution on the remote host for its own output and return code.

Compiling

If you are having any problems compiling on your system, please let us know (preferrably with fixes). Most users should be able to compile nrpe and the check_nrpe plugin with the following commands...

./configure
make all

HINT: ./configure --help

NOTE: If you're cloning from GitHub, you'll need to run autoconf first.

NOTE: Since the check_nrpe plugin and nrpe daemon run on different machines (the plugin runs on the Nagios host and the daemon runs on the remote host), you will have to compile the nrpe daemon on the target machine.

Installing

You have a few options here. The binaries created from make all were placed in your src/ directory. You can either copy these where they need to be, or you can run any of the following make install options:

• make install-groups-users

  Add the users and groups sepcified during ./configure. Defaults to nagios and nagios, respectively. You can override these with the ./configure --with-nrpe-user=USER --with-nrpe-group=GROUP.

• make install

  This will run both install-plugin and install-daemon.

• make install-plugin

  This will install the plugin by default in /usr/local/nagios/libexec. You can override this behavior by using the --with-pluginsdir=DIR flag during ./configure.

• make install-daemon

  This will install the plugin by default in /usr/local/nagios/bin. You can override this behavior by using the --prefix=DIR or --bindir=DIR flags during ./configure.

• make install-config

  This will install the sample config by default in /usr/local/nagios/etc. You can override this behavior by using the --with-pkgsysconfdir=DIR flag during ./configure.

• make install-inetd

  ./configure attempts to determine your inetd type. If it finds it, it will install the appropriate inetd script in the proper location. You can help it out with ./configure --with-inetd-type=TYPE where TYPE can be one of: inetd, xinetd, systemd, launchd, smf10, smf11.

• make install-init

  ./configure attempts to determine the appropriate init type. If it figures it out, will install the required startup script. You can help it out with ./configure --with-init-type=TYPE where TYPE can be one of: bsd, sysv, systemd, launchd, smf10, smf11, upstart, openrc.

If you used all the necessary ./configure flags, you shouldn't need to tweak your config file any at this point, and a simple service nrpe start or systemctl start nrpe.service should work just fine.

Configuring

A sample config file for the NRPE daemon are located in the sample-config/ subdirectory.

If you used the proper flags during ./configure, this file should contain all of the appropriate information as a starting point.

Running Under inetd or xinetd

If you plan on running nrpe under inetd or xinetd and making use of TCP wrappers, you need to add a line to your /etc/services file as follows (modify the port number as you see fit)

 nrpe            5666/tcp    # NRPE

The run make install-inetd to copy the appropriate file, or add the appropriate line to your /etc/inetd.conf.

NOTE: If you run nrpe under inetd or xinetd, the server_port and allowed_hosts variables in the nrpe configuration file are ignored.

• inetd

  After running make install-inetd, your /etc/inetd.conf file will contain lines similar to the following:

   # Enable the following entry to enable the nrpe daemon
   #nrpe stream tcp nowait nagios /usr/local/nagios/bin/nrpe nrpe -c /usr/local/nagios/etc/nr
   # Enable the following entry if the nrpe daemon didn't link with libwrap
   #nrpe stream tcp nowait nagios /usr/sbin/tcpd /usr/local/nagios/bin/nrpe -c /usr/local/nag
  

  Un-comment the appropriate line, then Restart inetd:

   /etc/rc.d/init.d/inet restart
  

  OpenBSD users can use the following command to restart inetd:

   kill -HUP `cat /var/run/inet.pid`
  

  Then add entries to your /etc/hosts.allow and /etc/hosts.deny file to enable TCP wrapper protection for the nrpe service. This is optional, although highly recommended.

• xinetd

  If your system uses xinetd instead of inetd, make install-inetd will create a file called nrpe in your /etc/xinetd.d directory that contains a file similar to this:

   # default: off
   # description: NRPE (Nagios Remote Plugin Executor)
   service nrpe
   {
       disable         = yes
       socket_type     = stream
       port            = @NRPE_PORT@
       wait            = no
       user            = nagios
       group           = nagios
       server          = /usr/local/nagios/bin/nrpe
       server_args     = -c /usr/local/nagios/etc/nrpe.cfg --inetd
       only_from       = 127.0.0.1
       log_on_failure  += USERID
   }
  

  • Replace disable = yes with disable = no

  • Replace the 127.0.0.1 field with the IP addresses of hosts which are allowed to connect to the NRPE daemon. This only works if xinetd was compiled with support for tcpwrappers.

  • Add entries to your /etc/hosts.allow and /etc/hosts.deny file to enable TCP wrapper protection for the nrpe service. This is optional, although highly recommended.

  • Restart xinetd:

     /etc/rc.d/init.d/xinetd restart
    

Configuring Things On The Nagios Host

Examples for configuring the nrpe daemon are found in the sample nrpe.cfg file included in this distribution. That config file resides on the remote host(s) along with the nrpe daemon. The check_nrpe plugin gets installed on the Nagios host. In order to use the check_nrpe plugin from within Nagios, you will have to define a few things in the host config file. An example command definition for the check_nrpe plugin would look like this:

define command{
    command_name           check_nrpe
    command_line           /usr/local/nagios/libexec/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
    }

In any service definitions that use the nrpe plugin/daemon to get their results, you would set the service check command portion of the definition to something like this (sample service definition is simplified for this example):

define service{
    host_name              someremotehost
    service_description    someremoteservice
    check_command          check_nrpe!yourcommand
    ... etc ...
    }

where yourcommand is a name of a command that you define in your nrpe.cfg file on the remote host (see the docs in the sample nrpe.cfg file for more information).

License Notice

NRPE - Nagios Remote Plugin Executor

Copyright (c) 2017 Nagios Enterprises

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

Questions?

If you have questions about this addon, or encounter problems getting things working along the way, your best bet for an answer or quick resolution is to check the Nagios Support Forums.