With IPHost Network Monitor you can run simple snmp requests against a Fortinet device in your network.
fnSysMonMemUsage
fn Sys Monitor Memory Usage
1.3.6.1.4.1.12356.1.1.6.4
The current memory usage statistics
Back to FORTINET-MIB MIB page.
IPHost Network monitor allows you to monitor fnSysMonMemUsage on Fortinet device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Fortinet switches right now.