My Ubuntu 16 installation occasionally has weird rendering issues. How can I tell if I am in software rendering mode?
Running ubuntu-drivers devices outputs:
== cpu-microcode.py ==
driver : intel-microcode - distro non-free1 Answer
Your operating system is not using an Nvidia or AMD proprietary graphics driver, so your system is currently running in software rendering mode. If there was a proprietary graphics driver compatible with your computer's hardware available from the default Ubuntu repositories, then ubuntu-drivers devices would have listed it.
For more information read the answers to How to download all required Ubuntu drivers.
