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addons:nagios-nrpe

Set up and configure NRPE server on IPFire

NRPE (Nagios Remote Plugin Executor) is an application to run Nagios plugins on a remote server and query the result via an encrypted connection. It is useful for monitoring remote machines which cannot provide system details via SNMP or similair, or shouln't do that because of security reasons.

The NRPE package is not equal to the Nagios one, although it requires this because of some dependencies. Please disable the Nagios server (which is running a web interface) if you don't need it.

Install add-ons

To run a NRPE server on IPFire, you need to install the nagios_nrpe package at the pakfire page. The NRPE server package requires the basic Nagios package too, so make sure to install this one as well, in case it was not installed automatically.

Prevent Nagios from starting

To prevent Nagios from starting automatically on boot, go to the services status page. Scroll down to the “addon - services” table and uncheck the “boot” box for the entry called “nagios”.

This step is important to avoid security risks by running an unused service. For more information related to this topic, please have a look at the IPFire security hardening guide.

Configure NRPE

The NRPE package requires a lot of manual configuration, even adding init scripts for start and shutdown during booting or system halting.

Set up init script

Download the following script and place it to /etc/init.d/nrpe. Ensure it is readable for everyone, but not writeable (permission 755).

nrpe
#!/bin/sh
# Begin $rc_base/init.d/nrpe
 
. /etc/sysconfig/rc
. $rc_functions
 
NRPEBIN=/usr/bin/nrpe
NRPECFG=/etc/nagios/nrpe.cfg
 
case "$1" in
start)
boot_mesg "Starting nrpe..."
loadproc $NRPEBIN -c $NRPECFG -d
;;
 
stop)
boot_mesg "Stopping nrpe..."
killproc $NRPEBIN
rm -f /var/run/nrpe.pid
;;
 
restart)
$0 stop
sleep 1
$0 start
;;
 
status)
statusproc $NRPEBIN
;;
 
*)
echo "Usage: $0 {start|stop|restart|status}"
exit 1
;;
esac
 
# End $rc_base/init.d/nrpe

Then, run

chmod +x /etc/init.d/nrpe

to mark this script as executable.

To start and stop NRPE during booting or shutdown, execute the following commands:

ln -s /etc/init.d/nrpe /etc/rc.d/rc3.d/S40nrpe
ln -s /etc/init.d/nrpe /etc/rc.d/rc0.d/K20nrpe
ln -s /etc/init.d/nrpe /etc/rc.d/rc6.d/K20nrpe

After that, NRPE will be started at runlevel 3 and stopped at runlevels 0 (halt) and 6 (reboot).

Set up configuration

Next, place the following example configuration to /etc/nagios/nrpe.cfg. Again, make sure it is readable for everyone, but only writable to its owner, which should be root.

nrpe.cfg
#############################################################################
# Sample NRPE Config File 
# Written by: Ethan Galstad (nagios@nagios.org)
# 
# Last Modified: 11-23-2007
#
# NOTES:
# This is a sample configuration file for the NRPE daemon.  It needs to be
# located on the remote host that is running the NRPE daemon, not the host
# from which the check_nrpe client is being executed.
#############################################################################
 
 
# LOG FACILITY
# The syslog facility that should be used for logging purposes.
 
log_facility=daemon
 
 
 
# PID FILE
# The name of the file in which the NRPE daemon should write it's process ID
# number.  The file is only written if the NRPE daemon is started by the root
# user and is running in standalone mode.
 
pid_file=/var/run/nrpe.pid
 
 
 
# PORT NUMBER
# Port number we should wait for connections on.
# NOTE: This must be a non-priviledged port (i.e. > 1024).
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd
 
server_port=5666
 
 
 
# SERVER ADDRESS
# Address that nrpe should bind to in case there are more than one interface
# and you do not want nrpe to bind on all interfaces.
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd
 
#server_address=127.0.0.1
 
 
 
# NRPE USER
# This determines the effective user that the NRPE daemon should run as.  
# You can either supply a username or a UID.
# 
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd
 
nrpe_user=nobody
 
 
 
# NRPE GROUP
# This determines the effective group that the NRPE daemon should run as.  
# You can either supply a group name or a GID.
# 
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd
 
nrpe_group=users
 
 
 
# ALLOWED HOST ADDRESSES
# This is an optional comma-delimited list of IP address or hostnames 
# that are allowed to talk to the NRPE daemon. Network addresses with a bit mask
# (i.e. 192.168.1.0/24) are also supported. Hostname wildcards are not currently 
# supported.
#
# Note: The daemon only does rudimentary checking of the client's IP
# address.  I would highly recommend adding entries in your /etc/hosts.allow
# file to allow only the specified host to connect to the port
# you are running this daemon on.
#
# NOTE: This option is ignored if NRPE is running under either inetd or xinetd
 
allowed_hosts=127.0.0.1
 
 
 
# COMMAND ARGUMENT PROCESSING
# This option determines whether or not the NRPE daemon will allow clients
# to specify arguments to commands that are executed.  This option only works
# if the daemon was configured with the --enable-command-args configure script
# option.  
#
# *** ENABLING THIS OPTION IS A SECURITY RISK! *** 
# Read the SECURITY file for information on some of the security implications
# of enabling this variable.
#
# Values: 0=do not allow arguments, 1=allow command arguments
 
dont_blame_nrpe=0
 
 
 
# COMMAND PREFIX
# This option allows you to prefix all commands with a user-defined string.
# A space is automatically added between the specified prefix string and the
# command line from the command definition.
#
# *** THIS EXAMPLE MAY POSE A POTENTIAL SECURITY RISK, SO USE WITH CAUTION! ***
# Usage scenario: 
# Execute restricted commmands using sudo.  For this to work, you need to add
# the nagios user to your /etc/sudoers.  An example entry for alllowing 
# execution of the plugins from might be:
#
# nagios          ALL=(ALL) NOPASSWD: /usr/lib/nagios/plugins/
#
# This lets the nagios user run all commands in that directory (and only them)
# without asking for a password.  If you do this, make sure you don't give
# random users write access to that directory or its contents!
 
# command_prefix=/usr/bin/sudo 
 
 
 
# DEBUGGING OPTION
# This option determines whether or not debugging messages are logged to the
# syslog facility.
# Values: 0=debugging off, 1=debugging on
 
debug=0
 
 
 
# COMMAND TIMEOUT
# This specifies the maximum number of seconds that the NRPE daemon will
# allow plugins to finish executing before killing them off.
 
command_timeout=60
 
 
 
# CONNECTION TIMEOUT
# This specifies the maximum number of seconds that the NRPE daemon will
# wait for a connection to be established before exiting. This is sometimes
# seen where a network problem stops the SSL being established even though
# all network sessions are connected. This causes the nrpe daemons to
# accumulate, eating system resources. Do not set this too low.
 
connection_timeout=300
 
 
 
# WEEK RANDOM SEED OPTION
# This directive allows you to use SSL even if your system does not have
# a /dev/random or /dev/urandom (on purpose or because the necessary patches
# were not applied). The random number generator will be seeded from a file
# which is either a file pointed to by the environment valiable $RANDFILE
# or $HOME/.rnd. If neither exists, the pseudo random number generator will
# be initialized and a warning will be issued.
# Values: 0=only seed from /dev/[u]random, 1=also seed from weak randomness
 
#allow_weak_random_seed=1
 
 
 
# INCLUDE CONFIG FILE
# This directive allows you to include definitions from an external config file.
 
#include=<somefile.cfg>
 
 
 
# INCLUDE CONFIG DIRECTORY
# This directive allows you to include definitions from config files (with a
# .cfg extension) in one or more directories (with recursion).
 
#include_dir=<somedirectory>
#include_dir=<someotherdirectory>
 
 
 
# COMMAND DEFINITIONS
# Command definitions that this daemon will run.  Definitions
# are in the following format:
#
# command[<command_name>]=<command_line>
#
# When the daemon receives a request to return the results of <command_name>
# it will execute the command specified by the <command_line> argument.
#
# Unlike Nagios, the command line cannot contain macros - it must be
# typed exactly as it should be executed.
#
# Note: Any plugins that are used in the command lines must reside
# on the machine that this daemon is running on!  The examples below
# assume that you have plugins installed in a /usr/local/nagios/libexec
# directory.  Also note that you will have to modify the definitions below
# to match the argument format the plugins expect.  Remember, these are
# examples only!
 
 
# The following examples use hardcoded command arguments...
 
command[check_users]=/usr/lib/nagios/check_users -w 5 -c 10
command[check_load]=/usr/lib/nagios/check_load -w 3,3,3 -c 10,10,10
command[check_zombie_procs]=/usr/lib/nagios/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/lib/nagios/check_procs -w 150 -c 200 
 
# The following examples allow user-supplied arguments and can
# only be used if the NRPE daemon was compiled with support for 
# command arguments *AND* the dont_blame_nrpe directive in this
# config file is set to '1'.  This poses a potential security risk, so
# make sure you read the SECURITY file before doing this.
 
#command[check_users]=/usr1/nagios/libexec/check_users -w $ARG1$ -c $ARG2$
#command[check_load]=/usr1/nagios/libexec/check_load -w $ARG1$ -c $ARG2$
#command[check_disk]=/usr1/nagios/libexec/check_disk -w $ARG1$ -c $ARG2$ -p $ARG3$
#command[check_procs]=/usr1/nagios/libexec/check_procs -w $ARG1$ -c $ARG2$ -s $ARG3$
 
#EOF

Adjust this configuration file to the needs of your network. For example, adjust the “allowed servers” field and the command definitions.

Do not enable the external command arguments since it is a security risk. Although frequently recommended in other NRPE tutorials, this method makes injecting (shell)code remotely very easy.

It is strongly recommended not to enable this technique but set accurate command definitions which satisfy the circumstances.

In case you are running Guadrian on your IPFire machine, it is recommended to add your monitoring system to the list of hosts that will never be blocked. For example, monitoring the IPFire SSH daemon causes false-positives and will lead Guardian to block the monitoring systems IP.

That's it, your NRPE server is now ready to start and to work properly.

Acknowledgements

Nearly all parts of this guide are taken from this forum branch (german only). Many thanks to pat_2015 for helping me with the NRPE server on IPFire!

In case of errors and questions, please report them to the forum branch, stay calm and wait for reply. ;-)

addons/nagios-nrpe.txt · Last modified: 2018/09/20 18:33 by Jon