Zabbix passive checks scheduling

For passive checks, it's based on the itemID and the "Update interval" field. The formula is:

itemID % "Update interval" = offset (a remaining after the division)

For example, if:

         itemid = 871089
Update interval = 3m

The bash can tell a countdown when the data collection is about to happen:

watch -n1 'echo $(( (871089 % 180 - ($(date +%s) % 180) + 180) % 180 ))'