====== NRPE installation and configuration ======

First install NRPE on the Nagios server and on the client to monitor.

On the client, if you have multiple ethernet adapter specify on which the NRPE demon will LISTEN (server_address=192.168.222.152)

Enable the log in verbose mode to be able to debug, once everything is right that can be changed.\\
Parameters: log_facility=daemon    and   debug=1

On the client start the nrpe demon 
  /etc/rc.d/init.d/nrpe start

On the Nagios server try to contact the client:
<cli prompt='#'>
[root@nagios objects]# /usr/lib/nagios/plugins/check_nrpe  -H 192.168.222.152
CHECK_NRPE: Error - Could not complete SSL handshake.
</cli>

You have to authorize the Nagios server to contact the client. On the client in /etc/nagios/nrpe.cfg 
  allowed_hosts=127.0.0.1,192.168.222.168
  
Restart you nrpe demon on the client:
  /etc/rc.d/init.d/nrpe restart
  
On the Nagios server try to contact the client:
<cli prompt='#'>
[root@nagios objects]# /usr/lib/nagios/plugins/check_nrpe  -H 192.168.222.152
NRPE v2.15
</cli>

**Now it work !**

Try another test:
<cli prompt='#'>
[root@nagios objects]# /usr/lib/nagios/plugins/check_nrpe  -H 192.168.222.152 -c check_load
OK - load average: 1.30, 1.35, 1.44|load1=1.300;15.000;30.000;0; load5=1.350;10.000;25.000;0; load15=1.440;5.000;20.000;0; 
[root@nagios objects]# /usr/lib/nagios/plugins/check_nrpe  -H 192.168.222.152 -c check_total_procs
PROCS OK: 62 processes | procs=62;150;200;0;
</cli>

Threshold and command are defined on the client into /etc/nagios/nrpe.cfg
  ...
  command[check_users]=/opt/freeware/lib/nagios/plugins/check_users -w 5 -c 10
  command[check_load]=/opt/freeware/lib/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
  command[check_hda1]=/opt/freeware/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/hda1
  command[check_zombie_procs]=/opt/freeware/lib/nagios/plugins/check_procs -w 5 -c 10 -s Z
  command[check_total_procs]=/opt/freeware/lib/nagios/plugins/check_procs -w 150 -c 200 

Now you can add on the Nagios server into **command.cfg**
  # 'check_nrpe_load' command definition
  define command{
        command_name    check_nrpe_load
        command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c check_load
        }

  # 'check_nrpe_procs' command definition
  define command{
        command_name    check_nrpe_procs
        command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c check_total_procs
        }

And in **services.cfg**
  define service{
        use                             aix-service
        hostgroup_name                  aix
        service_description             CPU Load
        check_command                   check_nrpe_load
        }
  
  define service{
        use                             aix-service
        hostgroup_name                  aix
        service_description             Total Processes
        check_command                   check_nrpe_procs
        }

<cli prompt='#'>
# nagios -v /etc/nagios/nagios.cfg
# /etc/rc.d/init.d/nagios reload
</cli>

===== Compile NRPE for AIX =====

On AIX binary files or RPM start NRPE as root

To change it, recompile **nrpe.c**

Get latest source from github, and modify using the followin paragraph, starting line 2587 on version 4.1.0

<code>
#endif
/* Last Modified: 2022-07-18 line 2587 */

                        if (full_drop) {
                                /*setuid(uid) doesn’t work on aix but doesn’t return -1 either*/
                                if (setuid(uid) == -1) 
                                        logit(LOG_ERR, "Warning: Could not set UID=%d", (int)uid);
                                /*setuid(uid) returned anything but -1*/
                                else 
                                        /*if the current uid still isn’t geteuid() setuid failed and thus we SETEUID(uid)*/
                                        if (uid != geteuid()) 
                                                if (SETEUID(uid) == -1)
                                                        logit(LOG_ERR, "Warning: Could not set effective UID=%d", (int)uid);

                        } else if (SETEUID(uid) == -1)
                                logit(LOG_ERR, "Warning: Could not set effective UID=%d", (int)uid);
                }
</code>