So all of a sudden, after a week of using it, I get an error message on my zabbix server
gui (http://localhost/zabbix/.)
The error says: Zabbix serve
In my case it happens when introducing host with templates, graphs,trigger etc, the server falls. The problem was that by default the cache is at 128k and you have to change it.
sudo nano /etc/zabbix/zabbix-server.conf
Uncheck # Sizecache and add 32M for example.
Cachesize=32M
restart service and voila!! server working
service zabbix-server start