Setting up Nagios on a Debian Server to Remotely Monitor an Untangle Server

These instructions are a modified version of those found on the Untangle Forum.  They have been slightly altered to match Debian's Nagios configuration and my needs.

These instructions assume that you already have Nagios installed and configured on your Debian server.  At some point I may write instructions for doing so, but reading the documentation that comes with the Nagios packages and found on nagios.org should be sufficient.

Add a Packet Filter Rule

We need to add a packet filter rule to the Untangle server so that it will allow the Nagios server to query information.  This is done through the Untangle web interface.  These specific instructions assume you have advanced networking options enabled.  They are written for Untangle v. 6.1.

Go to Config, Networking, Advanced, Packet Filter.  Add a new packet rule with the following options:

Enabled:  Checked
Description:  NRPE (Nagios Remote Plugin Executor)
Action:  Pass
Source Address:  10.0.0.20
Source Interface:  Internal
Destination Local
Destination Address:  10.0.0.1
Destination Port:  5666
Protocol:  TCP

The Source Address is the Debian Nagios server.  The Destination Address is the IP address of the Untangle Server.  The Destination Port is the port used by NRPE to communicate between Nagios server and client.  The default destination port is 5666.  All communication between the server and client use TCP.  If you are connecting from the External, DMZ, or VPN interfaces, you'll need to modify the Source Interface.

Install NRPE on the Untangle Server

Open a terminal on (or connect by SSH to) the Untangle Server.  Edit the sources.list file:

nano /etc/apt/sources.list

All of the repositories in this list are commented out.  Uncomment the first repository and save the file.  sources.list should then look something like this:

deb http://ftp.debian.org/debian lenny main contrib non-free
# Commented by Untangle: deb http://security.debian.org lenny/updates main contrib non-free
# Commented by Untangle: deb http://volatile.debian.org/debian-volatile lenny/volatile main contrib non-free
#deb http://www.backports.org/debian lenny-backports main contrib non-free

Update the list of available packages:

apt-get update

Install nagios-nrpe-server and nagios-plugins

apt-get install nagios-nrpe-server nagios-plugins

This will pull in several other required packages (14 in all the last time I did the install).  In NRPE parlance, the "server" is installed on the machine you are monitoring and the "client" is installed on the Nagios server.

Now we can edit the sources.list file and return it to it's original state:

nano /etc/apt/sources.list

The resulting sources.list should look some like the following:

# Commented by Untangle: deb http://ftp.debian.org/debian lenny main contrib non-free
# Commented by Untangle: deb http://security.debian.org lenny/updates main contrib non-free
# Commented by Untangle: deb http://volatile.debian.org/debian-volatile lenny/volatile main contrib non-free
#deb http://www.backports.org/debian lenny-backports main contrib non-free

Save the file and reupdate the list of available packages:

apt-get update

Configure NRPE on the Untangle Server

Edit /etc/nagios/nrpe.conf.

nano /etc/nagios/nrpe.conf

Set the server_address to the IP address you want NRPE to bind to on the Untangle server.  If you want it to bind to all addresses, leave this command commented out.

server_address=10.0.0.1

Change allowed_hosts to the IP address of the Nagios server:

allowed_hosts=10.0.0.20

Turn on debugging (if desired):

debug=1

Add a command to check the swap utilization:

command[check_swap]=/usr/lib/nagios/plugins/check_swap -w 20% -c 10%

Edit the command for checking the hard drive so that it works with SATA drives instead of IDE drives (if your server uses SATA).  To do this, replace both instances of hda1 with sda1.  The resulting command will look as follows:

command[check_sda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/sda1

Save nrpe.conf.  My resulting file looks like this:

############################################################################
# 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=10.0.0.1

# 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=nagios

# 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=nagios

# ALLOWED HOST ADDRESSES
# This is an optional comma-delimited list of IP address or hostnames
# that are allowed to talk to the NRPE daemon.
#
# 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=10.0.0.20

# 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=1

# 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
# 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_swap]=/usr/lib/nagios/plugins/check_swap -w 20% -c 10%
command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_sda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/sda1
command[check_zombie_procs]=/usr/lib/nagios/plugins/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/lib/nagios/plugins/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]=/usr/lib/nagios/plugins/check_users -w $ARG1$ -c $ARG2$
#command[check_load]=/usr/lib/nagios/plugins/check_load -w $ARG1$ -c $ARG2$
#command[check_disk]=/usr/lib/nagios/plugins/check_disk -w $ARG1$ -c $ARG2$ -p $ARG3$
#command[check_procs]=/usr/lib/nagios/plugins/check_procs -w $ARG1$ -c $ARG2$ -s $ARG3$

# local configuration:
# if you'd prefer, you can instead place directives here
include=/etc/nagios/nrpe_local.cfg

# you can place your config snipplets into nrpe.d/
include_dir=/etc/nagios/nrpe.d/

Restart the NRPE service:

/etc/init.d/nagios-nrpe-server restart

Configure the (Debian) Nagios Server

Now it is time to configure the Nagios server.  These instructions were written specifically for Debian's Nagios packages version 3.0.6-3 with nagios-nrpe-plugin version 2.12-3 and nagios-plugins 1.4.12-5, but they should work resonably well with other versions.  As always, your mileage may vary.

Make sure you have nagios-nrpe-plugin installed.  This package provides /usr/lib/nagios/plugins/check_nrpe, which we will be using shortly.

Create a file named /etc/nagios3/conf.d/untangle.cfg with the following contents:

#Host Definition
define host{
        use                     generic-host
        host_name               Untangle
        alias                   Untangle Server
        address                 10.0.0.1
        }

# Service Definitions
define service{
        use                     generic-service
        host_name               Untangle
        service_description     CPU Load
        check_command           check_nrpe_1arg!check_load
        }

define service{
        use                     generic-service
        host_name               Untangle
        service_description     Swap Drive Usage
        check_command           check_nrpe_1arg!check_swap
        }

define service{
        use                     generic-service
        host_name               Untangle
        service_description     Free Disk Space
        check_command           check_nrpe_1arg!check_sda1
        }

define service{
        use                     generic-service
        host_name               Untangle
        service_description     Number of Users
        check_command           check_nrpe_1arg!check_users
        }

define service{
        use                     generic-service
        host_name               Untangle
        service_description     Number of Zombie Processes
        check_command           check_nrpe_1arg!check_zombie_procs
        }

define service{
        use                     generic-service
        host_name               Untangle
        service_description     Total Processes
        check_command           check_nrpe_1arg!check_total_procs
        }

We are using check_nrpe_1arg to match the syntax in Debian's /usr/lib/nagios/plugins/check_nrpe.  check_nrpe pulls the arguments from the .cfg file and sends them to the monitored machine.  If you'll notice in the above nrpe.conf, we have that configuration disabled (default setting) and we have hardcoded in the arguments for each command.  Hence, we need to use check_nrpe_1arg or we will get an error message when we run the checks.

You may change the host_name to anything of your choice (you'll want to make sure they are all the same throughout the file).  You'll also want to update the address in the define host section to match that of your Untangle server.

Edit /etc/nagios3/conf.d/hostgroups_nagios2.cfg and add the following section to define an Untangle Server group.  This step is optional, but is nice if you are going to monitor more than one Untangle server.  (Also, you might want to rename the file to something more logical, like hostgroups.cfg.)

define hostgroup {
        hostgroup_name  untangle-servers
                alias           Untangle Servers
                members         Untangle
        }

If you have more than one Untangle Server in the group, it will look like the following:

define hostgroup {
        hostgroup_name  untangle-servers
                alias           Untangle Servers
                members         Untangle1, Untangle2, Untangle3
        }

Restart the Nagios service to apply the changes:

/etc/init.d/nagios3 restart

Load up the Nagios website and see if you managed to type everything correctly.  :)