Murrine

I believe he is using Liberation Sans from the Liberation suite made by redhat. They made a Sans, Sans Serif and a Mono font that look better than Arial, Times and Courier If you have Ubuntu or Debian you can install with:

sudo apt-get install ttf-liberation
Or if not you can download and extract them to the hidden .font folder in the home directory. (in nautilus View->Show Hidden Files)

https://www.redhat.com/f/fonts/liberation-fonts.tar.gz