I bought a case for the pi, and it came with a fan. The fan is plugged into pins 2 and 3 (I think?) of the GPIO header. It runs full time, and at full speed. Is there a way to shut it off via software, even SSH if need be? I’ll have someone sleeping near the thing and it would be great to have it quiet at night. Thank you!
You can just plug it out, pis don’t need active cooling, unless you do some computation stuff 24/7.
Fans plugged directly into power can not be controlled via software.
The fan is probably plugged into pins 4 (5 volts) and 6 (ground). If you plug into pins 1 (3.3 volts) and 6 the fan will run slower and reduce noise significantly. I did this on a couple of PI projects and the fan noise was not significant.
As doghouse says you may not need a fan at all. But that depends on the case and environment. While it is generally cooler at night, if you need a fan, you probably need to run it 24/7 at least at reduced speed durning the night.
You might also look into a speed control based on ambient temperature.
Think about other electronics in the vicinity that might also need cooling. AC Infinity makes a series of cooling fans intended for use in home theater applications and are very quiet. I used one in my travel trailer to cool my electronics bay: Cerbo, Multi, MPPT, etc.