• I followed this guide for setting up the Nagios client.
  • Upgraded all packages: 
    dnf upgrade -y
  • Installed required packages: 
    dnf install -y gcc glibc glibc-common gd gd-devel make net-snmp openssl-devel tar wget
dnf install -y make gettext automake autoconf wget openssl-devel net-snmp net-snmp-utils
  • Created my nagios user: 
    useradd nagios
passwd nagios
  • Installed all available plugins:
  • Changed into /tmp: 
    cd /tmp
  • Pulled the latest plugins tarball: 
    wget --output-document="nagios-plugins.tar.gz" $(wget -q -O - https://api.github.com/repos/nagios-plugins/nagios-plugins/releases/latest  | grep '"browser_download_url":' | grep -o 'https://[^"]*')
  • Ran tar -zxf: 
    tar zxf nagios-plugins.tar.gz
  • Changed directories: 
    cd /tmp/nagios-plugins-*
  • Compiled the packages: 
    ./configure
make
make install
  • Set directory permissions for the nagios user: 
    chown nagios.nagios /usr/local/nagios
chown -R nagios.nagios /usr/local/nagios/libexec
  • Pulled down the latest version of the nrpe plugin, which at the time of writing is 4.1.3: 
    wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.3/nrpe-4.1.3.tar.gz
  • Ran tar -zxf: 
    tar -zxf ./nrpe-4.1.3.tar.gz
  • Changed directories: 
    cd nrpe-4.1.3/
  • Compiled and installed nrpe: 
    ./configure
make all
  • Installed the plugin daemon and the sample config files: 
    make install-plugin
make install-daemon
make install-config
  • Install the NRPE daemon as a systemd service: 
    make install-init
  • Configured the NRPE plugin’s configuration file at /usr/local/nagios/etc/nrpe.cfg and added the address of my Nagios server: 
    sed -i 's/allowed_hosts=127.0.0.1,::1/allowed_hosts=127.0.0.1,10.25.96.5/' /usr/local/nagios/etc/nrpe.cfg
  • Enabled and then started the nrpe service: 
    systemctl enable --now nrpe
  • I observed this started correctly from journalctl -exu nrpe and netstat -at | grep nrpe: ``` Jan 20 05:51:26 rocky-linux-810-non-fips-nagios-client nrpe[74633]: Starting up daemon Jan 20 05:51:26 rocky-linux-810-non-fips-nagios-client nrpe[74633]: Server listening on 0.0.0.0 port 5666. Jan 20 05:51:26 rocky-linux-810-non-fips-nagios-client nrpe[74633]: Server listening on :: port 5666. Jan 20 05:51:26 rocky-linux-810-non-fips-nagios-client nrpe[74633]: Listening for connections on port 5666 Jan 20 05:51:26 rocky-linux-810-non-fips-nagios-client nrpe[74633]: Allowing connections from: 127.0.0.1,10.25.96.5

netstat -at | grep nrpe tcp 0 0 0.0.0.0:nrpe 0.0.0.0:* LISTEN
tcp6 0 0 [::]:nrpe [::]:* LISTEN

* Opened up required ports in the Firewall:

firewall-cmd –zone=public –add-port=5666/tcp –permanent firewall-cmd –reload

* I ran `/usr/local/nagios/libexec/check_nrpe -H 127.0.0.1` to also check that `check_nrpe` was working correctly:

[root@rocky-linux-810-non-fips-nagios-client nrpe-4.1.3]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 NRPE v4.1.3

* Confirmed from multiple commands that the client was working as expected:

[root@rocky-linux-810-non-fips-nagios-client nrpe-4.1.3]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_users USERS OK - 1 users currently logged in |users=1;5;10;0

[root@rocky-linux-810-non-fips-nagios-client nrpe-4.1.3]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_load OK - load average per CPU: 0.00, 0.00, 0.00|load1=0.000;0.150;0.300;0; load5=0.000;0.100;0.250;0; load15=0.003;0.050;0.200;0;

[root@rocky-linux-810-non-fips-nagios-client nrpe-4.1.3]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_total_procs PROCS OK: 140 processes | procs=140;150;200;0;

[root@rocky-linux-810-non-fips-nagios-client nrpe-4.1.3]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_zombie_procs PROCS OK: 0 processes with STATE = Z | procs=0;5;10;0; ```

Updated: