DNHYPER: Install NAGIOS core on DEBIAN 12

First you must install Debian 12 with no GUI and no webserver. Just the base and the SSH server. Try using another username for the base linux than nagios.

Install sudo, as on debian it is not a base package like on ubuntu and later you'll need it.

If you used a virtual machine, I recommend to start first with a bridged adapter network controller, so you don't need to go through double routing or port forwarding straight for any apt upgrade/install/update. If you were a network guru, do as you wish. The non gui server needs no resource, so 1 or 2 processor, 2 gigs of ram and 20gigs of space would be more than enough.

To copy commands into a VM, simply use SSH connection on powershell or putty:
ssh 192.168.1.55

NOTES

https://support.nagios.com/kb/article/nagios-core-installing-nagios-core-from-source-96.html#Debian

------------------------
LINUX USER DURING INSTALL:
   PSWD SU : Azerty

   user : DNHYPER
   pswd : Azerty
-------------------------
LINUX User NAGIOS:
       user: nagios
       pswd: Azerty
-------------------------
WEB LOGIN (set up later):
   user: nagiosadmin
   pswd: Azerty
-------------------------

COMMANDS

INSTALL SUDO:
    apt-get install sudo

INSTALL APACHE2 PHP ETC:
    apt-get install apache2 php php-gd php-imap php-curl php-mcrypt

INSTALL PERL AND IT'S LIBRARIES:
   apt-get install libxml-libxml-perl libnet-snmp-perl libperl-dev libnumber-format-perl libconfig-inifiles-perl libdatetime-perl libnet-dns-perl

INSTALL GRAPHICAL LIBRARIES:
   apt-get install libpng-dev libjpeg-dev libgd-dev

INSTALL CoMPILATION UTILS of MAKE and AUTOCONF WITH OTHER UTILS:
   apt-get install -y autoconf gcc libc6 make wget unzip apache2 apache2-utils php libgd-dev
   apt-get install openssl libssl-dev

CREATE USER NAGIOS + PSWD:
   useradd -m -p $(openssl passwd Azerty) nagios

CREATE GROUP NAGCMD:
   groupadd nagcmd

Add user NAGIOS and user www-data to group NAGCMD
   usermod -a -G nagcmd nagios
   usermod -a -G nagcmd www-data (it is running apache2)

CREATE A DOWNLOAD DIRECTORY:
   mkdir /home/nagios/downloads

DOWNLOAD NAGIOS to the DOWNLOAD DIRECTORY:
   cd /home/nagios/downloads
    wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.5.1.tar.gz

DECOMPRESS ARCHIVE NAGIOS:
    tar -zxvf nagios-4.5.1.tar.gz

ENTER DIRECTORY:
   cd nagios-4.5.1

DEFAULT WEB ACCESS + GROUP DIRECTORY:
    ./configure --with-httpd-conf=/etc/apache2/sites-enabled --with-command-group=nagcmd

LAUNCH COMPILATION:
    make all

CREATE NAGIOS ARBORESCENCE:
    make install

INSTALL NAGIOS SERVICE:
   make install-daemoninit

INSTALL NAGIOS PIPE:
   make install-commandmode

INSTALL CONFIG FILES:
   make install-config

INSTALL WEB-ADMIN INTERFACE:
   make install-webconf

MODULES REWRITE AND CGI OF APACHE ENABLE:
   a2enmod rewrite
   a2enmode cgi

CONFIGURE ADMIN ACCESS NAGIOS by APACHE - user:nagiosadmin pswd:Azerty:
    htpasswd -cb /usr/local/nagios/etc/htpasswd.users nagiosadmin Azerty

CONFIG the CONFIG RIGHTS to nagios USER:
   chown -R nagios:nagcmd /usr/local/nagios

RESTART APACHE and START NAGIOS:
   systemctl restart apache2
   systemctl start nagios