setting CPU frequency

[Richard Kimber]

My CPU will run up to 4.4Ghz but I want to limit it to a maximum of
4.0Ghz to avoid overheating problems.

When I try:
sudo cpufreq-set -u 4.0Ghz
or indeed any cpufreq-set command, I get:-

Error setting new values. Common errors:
- Do you have proper administration rights? (super-user?)
- Is the governor you requested available and modprobed?
- Trying to set an invalid policy?
- Trying to set a specific frequency, but userspace governor is not
available, for example because of hardware which cannot be set to a
specific frequency or because the userspace governor isn't loaded?

What do I need to do to get cpufreq-set working? I'm using 16.04 with
4.13.0-26-generic

-- 
Richard Kimber