Fldigi is installed to run in Ubuntu with a "normal" process priority. This setting can be observed in the "System Monitor" application that is part of the Ubuntu operating System by selecting the "processes tab". Use the "view" setting to select "all processes" if you wish to see CPU load of all the processes running on your system.
Another, very interesting way to view processing load is to use the Linux command "TOP" in a terminal window. Load Fldigi, and decode signals and observed the results.
I change Fldigi process priority level from "normal" to "very high" for improved digital mode decoding performance on my computer system.
Process priority can only be changed by a user as "root", but you can make a very simple edit to the "limits.conf" file as root to give a non-root user permission to change the process priority of a application (fldigi).
#1 Open a Terminal
#2 Become "root" Type: sudo su (press enter) - (notice the space between sudo and su)
#3 Enter your password
#4 Type this at the command prompt (your prompt should look something like root@computername:/home/your-home-directory#)
nano /etc/security/limits.conf (press enter) - (nano is a text editor)
#5 Scroll down to the bottom of the limits.conf file using the down arrow key. Go to the very bottom, past the line that states "# end of file".
#6 Add this to the limits.conf file:
username - nice -20 (user name is YOUR sign-on user name that you use with your password to log on to your system). Notice the dashes!
Notice the examples above the "# end of file line". Line up your entry to match those examples.
#7 Save your entries to the file by pressing: Ctrl O then press "Enter" (Control and the letter O).
#8 Exit Nano: Press Ctrl X to exit.
#9 Type exit (Press enter) to exit root.
IF YOU MAKE A MISTAKE, CLOSE THE TEXT EDITOR (NANO) BY PRESSING "Ctrl and X" AND NO CHANGES WILL BE MADE. THEN JUST START OVER AGAIN.
#10 How to make the Process Priority change work:
When you boot into your graphic user interface, start fldigi, and then open "System Monitor", and then click on the processes tab and find Fldigi listed among all the current system processes running. Highlight fldigi and click on it. Then right click and select "Change Priority", and select "Very High". That's it!
But... This change will only last for this one session, when you reboot, Fldigi will revert back to normal process priority. You must use the System Monitor application to change Fldigi process priority each time you start your computer. It's easy! Again... Start Fldigi, start System Monitor, change Fldigi process priority to "Very High". Done! I would suggest you close system monitor, because it is a high load resource application. Use the Linux command "top" in a terminal window to view processes in the order of CPU usage. This information can be used to understand decoding performance on YOUR system.
Real-time process have demanding process scheduling requirements, and such process should never be blocked by lower priority processes, they should have short response time, and these response times should have a minimum variance. Common real-time programs are applications that collect continuous streams of data and process that data in real time, like Fldigi does.
I have read posts that Fldigi has very high resource requirements. This is simply not true! Compared to what other digital mode application? Any application that is sampling a data stream, and is doing fast Fourier transform needs CPU cycles. If you compare a digital mode decoder with a waterfall, and a decoder without a waterfall, the decoder without a waterfall will use less percentage of the CPU cycles. Compare Fldigi, and Xorg (video driver) with, and without the waterfall with the "top" command in a terminal. Also, when it is decoding, and not decoding.
Lastly... A word of caution. Just change the process priority of Fldigi only. You can degrade your system performance, or make your Linux system unstable, if you make process priority unbalanced.
My Linux system never, ever crashes. My research, experimentation, and monitoring of this adjustment to Fldigi process priority has improved the performance of Fldigi on my computer. The antenna, the transceiver, the interface, the data stream... processing.
Make Fldigi "boss" app!