Running Remote Commands for Nagios with NRPE · English

Nagios and NRPE logos
Image source

NRPE stands for Nagios Remote Plugin Executor. It lets you run commands on remote hosts. NRPE consists of two parts:

On the monitoring server running Nagios (Monitoring Host), you need to install the nrpe plugin.
On the remote hosts (Remote Host), you install the “nrpe-server” agent.

Diagram

We will use SSL for connections, so NRPE needs to be built with SSL support everywhere.

Installing the Agent on FreeBSD

I have already covered how to install Nagios on the Monitoring Host running FreeBSD.

cd /usr/ports/
portsnap fetch update
cd /usr/ports/net-mgmt/nrpe2
make config

Select:

[*] SSL   Enable SSL support (disables plain-text server)

Continue the installation:

make install clean
echo 'nrpe2_enable="YES"' >> /etc/rc.conf

Log in to the Monitoring Host and install the same port, since this port provides both the agent and the plugin. Just do not put nrpe2_enable in /etc/rc.conf.

Installing the Agent on Debian

I have already covered how to install Nagios on the Monitoring Host running Debian.

apt-get install nagios-nrpe-server

apt-get install nagios-nrpe-plugin

Configuring the Agent on the Remote Host

After installation, a configuration file will be available on the Remote Host:

on FreeBSD: /usr/local/etc/nrpe.cfg
on Debian: /etc/nagios/nrpe.cfg

Open it for editing. You need to allow the Monitoring Host to connect to the Remote Host:

server_address=203.0.113.42
allowed_hosts=127.0.0.1,203.0.113.41

Here, the IP addresses are:

“203.0.113.42” — the external address of the current server, i.e. the Remote Host;
“203.0.113.41” — the address of the Monitoring Host server.

In the same file, you can define commands that can be called from the Monitoring Host:

$ grep -E "^command\[check_" nrpe.cfg
command[check_users]=/usr/local/libexec/nagios/check_users -w 5 -c 10
command[check_load]=/usr/local/libexec/nagios/check_load -w 15,10,5 -c 30,25,20
command[check_root]=/usr/local/libexec/nagios/check_disk -w 20% -c 10% -p /
command[check_var]=/usr/local/libexec/nagios/check_disk -w 20% -c 10% -p /var
command[check_tmp]=/usr/local/libexec/nagios/check_disk -w 20% -c 10% -p /tmp
command[check_usr]=/usr/local/libexec/nagios/check_disk -w 20% -c 10% -p /usr
command[check_zombie_procs]=/usr/local/libexec/nagios/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/local/libexec/nagios/check_procs -w 150 -c 200

You can also specify two directives that allow you to include configuration files. This makes it better to move the commands into separate files:

# Присоединить определенный конфигурационный файл
include=/path/to/my_commands.cfg
# Или целый каталог
include_dir=/path/to/nrpe.d/

Now you can start the agent:

# Во FreeBSD
/usr/local/etc/rc.d/nrpe2 start

# На Debian
/etc/init.d/nagios-nrpe-server start

Configuring the Plugin on the Monitoring Host for FreeBSD

Log in to the Monitoring Host, open the file /usr/local/etc/nagios/objects/commands.cfg for editing, and add the following command:

# NRPE
define command{
    command_name    check_remote_command
    command_line    $USER1$/check_nrpe2 -H $HOSTADDRESS$ -c $ARG1$
    }

Now open the services file, for example /usr/local/etc/nagios/objects/remotehosts.cfg (which we created earlier), and add the external services:

define service{
    use                             remote-service
    hostgroups                      remote-servers
    service_description             Current Users
    check_command                   check_remote_command!check_users
    }
define service{
    use                             remote-service
    hostgroups                      remote-servers
    service_description             Zombie Processes
    check_command                   check_remote_command!check_zombie_procs
    }
define service{
    use                             remote-service
    hostgroups                      remote-servers
    service_description             Total Processes
    check_command                   check_remote_command!check_total_procs
    }

and so on.

Then restart Nagios for the changes to take effect:

/usr/local/etc/rc.d/nagios restart

Configuring the Plugin on the Monitoring Host for Debian

Log in to the Monitoring Host, go to the /etc/nagios-plugins/config directory, and open the file check_nrpe.cfg. You should see something like this:

# this command runs a program $ARG1$ with arguments $ARG2$
define command {
    command_name    check_nrpe
    command_line    /usr/lib/nagios/plugins/check_nrpe -H $HOSTADDRESS$ -c $ARG1$ -a $ARG2$
}
# this command runs a program $ARG1$ with no arguments
define command {
    command_name    check_nrpe_1arg
    command_line    /usr/lib/nagios/plugins/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}

Now open the services file, for example /etc/nagios3/conf.d/remotehosts.cfg (which we created earlier here and here), and add the external services:

define service{
    use                             remote-service
    hostgroups                      remote-servers
    service_description             Current Users
    check_command                   check_nrpe_1arg!check_users
    }
define service{
    use                             remote-service
    hostgroups                      remote-servers
    service_description             Zombie Processes
    check_command                   check_nrpe_1arg!check_zombie_procs
    }
define service{
    use                             remote-service
    hostgroups                      remote-servers
    service_description             Total Processes
    check_command                   check_nrpe_1arg!check_total_procs
    }

Then restart Nagios for the changes to take effect:

service nagios3 restart

I also recommend reading my post on common problems with NRPE.