Dear Fayez,
FLUKA usually takes all the memory it needs and uses the full computing power of a CPU. The only optimization you can do is increasing the number of jobs that are running in parallel on different cores (or CPUs). First you want to look up how many CPUs you PC has. You can do that by typing
lscpu
in your console. You get a bunch of info with one line reading
CPU(s): X
X is the number of cores available.
To use more than one at a time from FLAIR, you have to install the task-spooler (tsp) package
sudo apt-get install task-spooler
and activate it with
tsp -S Y
with Y the number of cores you want to run on, e.g. Y=5. (I suggest to choose Y less than your number of available CPUs X if you want to use your PC while waiting for FLUKA to finish). You might want to write this line into your ~/.bashrc file so you don’t have to activate it again after restarting your PC.
Next, in the Run tab of FLAIR, create as many spawns of your job as you made available to tsp (Y=5 in my example) and select tsp in the dropdown menu.
Starting the simulation should now run Y jobs in parallel, meaning you can decrease the number of cycles or primaries by a factor of Y and still get the same statistics