Please recommend the program for fan speed control on Linux 
Which fans? Just the fans on your graphics cards? Your CPU fan(s)? System chassis fans? Or are you looking for something like a Speedfan alternative for Linux?
If it's just for the graphics cards, do they have AMD or Nvidia GPUs?
Can be Speedfan alternative
And Linux Ubuntu
Back with Ubuntu 12.04, I used lmsensors (monitoring only) with another fan control script, perhaps those have been updated for current releases of Ubuntu. I don't remember if it supported controlling fans with voltage control, or if it only worked with PWM fans, so you'll want to look into that.
But, would like control fan in mining
I think they might have integrated support for the fan controlling script. (Back then, I had to obtain it separately.)
This is as recent as late 2016, so hopefully it'll get you started on your version of Ubuntu. https://help.ubuntu.com/community/SensorInstallHowto