Caclulated Item for Memory

[vahab]

Hi, I am using Zabbix 3.0.1 and trying to get the real memory usage in Zabbix and then make the graph.

The value that I am interested in is : used - buffers - cached

By using zabbix_get I see that zabbix has a value for each of those Items.

/usr/bin/zabbix_get -s <hostname> -k "vm.memory.size[total]"
12197720
/usr/bin/zabbix_get -s <hostname> -k "vm.memory.size[free]"
2889368
/usr/bin/zabbix_get -s <hostname> -k "vm.memory.size[buffers]"
36060
/usr/bin/zabbix_get -s <hostname> -k "vm.memory.size[cached]"
4338156
/usr/bin/zabbix_get -s <hostname> -k "vm.memory.size[used]"
9308352
/usr/bin/zabbix_get -s <hostname> -k "vm.memory.size[available]"
7263584

When I define a 'Calculated' item for a host and put a formula it works fine for 'buffers' but gives me an error when I enter cached in the formula.

This formula works without any error :
Formula : last("vm.memory.size[buffers]")
Type of Information : Numeric (unsigned)

But when I change the formula as following it gives an error after a while
Formula : last("vm.memory.size[cached]")
Type of Information : Numeric (unsigned)

Status : Not supported
Info : Cannot evaluate expression : expected numeric token at "vm.memory.size[cached]"

I am wondering what is different ,while both have numeric values and looks to have a value in Zabbix. Does anyone have an idea ?

Thank you !