I use Linux Mint, I downloaded this version of Blender “blender-2.79-linux-glibc219-x86_64.tar.bz2” but afert istalling it, in node editor material shift+a shader I don’t find the principled shader.
I’m running Mint and I downloaded the tarball and opened up 2.79 and the principled shader is there and works for me. Both with shift a and with the menu.
Seeing that your add menu is not in sorted alphabetically (blender’s default behaviour), makes me think that you or some addon have changed the NODE_##_category_SH_NEW_SHADER classes… Probably some addon that was coded for a previous Blender version where the Principled was not present.
Check the bpy.types if the ShaderNodeBsdfPrincipled class is there, or try to add it to your material through the python console with:
If you still need to use that addon, you may need to change the code accordingly to make it compatible with the new nodeitems_utils.py. Can you tell us which one was the culprit? we could patch it for 2.79+.
ohh yes… they use the nodeitems in a very unfriendly way…
Updating blend4web to the 17.12 will include the Principled in the add menu, but it will still block any 3rd party nodes you may have.