For those of you that don’t know you can use the ‘get system performance top <delay> <max_lines>’ command from the Fortigate CLI console to view the top running processes, and you can sort them by memory usage by pressing ‘m’, in order to assess what is causing the high memory usage on the device.
Note: This command was introduced from FortiOS firmware v4.0 MR2 and onwards.
For more information on how to use this command and how to assess the output please see page 109 on http://docs.fortinet.com/fgt/handbook/fortigate-troubleshooting-40-mr2.pdf
You can also use the commands:
Diag sys top
to show processes and
Diag sys kill 9 <PID> ?
to kill processes.