1. Run "sudo a2enmod cgi" or "sudo a2enmod cgid"
2. Check that you have CGI:
>$ grep -R LoadModule /etc/apache2 | grep mod_cgi
>/etc/apache2/mods-available/cgid.load:LoadModule cgid_module /usr/lib/apache2/modules/mod_cgid.so
>/etc/apache2/mods-available/cgi.load:LoadModule cgi_module /usr/lib/apache2/modules/mod_cgi.so
>/etc/apache2/mods-enabled/cgid.load:LoadModule cgid_module /usr/lib/apache2/modules/mod_cgid.so
3. Find where to put the scripts for Apache:
>$ grep cgi-bin /etc/apache2/conf-available/serve-cgi-bin.conf
>ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
><Directory "/usr/lib/cgi-bin">
4. Make sure that the script is executable: run "chmod +x a.sh".
5. Must have "Content-type: text/html" ( https://piped.smnz.de/watch?v=Jzcu4JheCtY ):
>$ sudo cat /usr/lib/cgi-bin/a.sh
>#!/bin/bash
>echo "Content-type: text/html"
>echo ""
>echo "Hello world"
6. Not needed I guess - in "/etc/apache2/apache2.conf":
><Directory "/var/www/html">
> Options +ExecCGI
> AddHandler cgi-script .cgi .pl .py .sh
></Directory>