Hi,
I’m about making a flask of Chanel No. 5 (eau de toilette), and in a test rendering there are rectangles in the glass. I applied Shading > Smooth, but the rectangles are still there. 
Here’s a test render. I rendered this via shell, and the command line is
blender -b Chanel\ No.\ 5\ 13p.blend -o //render_ -F PNG --engine CYCLES -x 1 -a
The render:
And here’s a screenshot of my Blender interface:
Please always provide an example .blend file for us to check…
Hm. Renders fine here…
You do have geometry issues, though. At the top the model kind of folds in on itself. Tab into Edit mode, hit A to select all and then W > Remove Doubles with merge distance of 0.020:
The model also has unapplied scale. In Object mode, select the bottle, then hit Ctrl+A > Scale.
I tried what you suggested, but the result is more or less the same. 
I tried rendering your scene (even without my changes) on different machines and don’t seem to be able to replicate the issue: No rectangles here…
Perhaps someone who also sees these artifacts can chime in.
If it renders ok on your machines, could there be something wrong with my Blender installation? I have Blender 2.79b installed on Ubuntu 18.04 LTS.
No idea. If I just open your file and hit render, I get this:
When you say ubuntu and 2.79b, the obvious question would be:
Is that an “official” Blender 2.79b from https://www.blender.org/ or some version from an ubuntu repo?
It’s from an Ubuntu repository. The splash screen says 2.79b. I have a 32-bit system. Can I use the official version from blender.org, or is this 64-bit?
You can download 32 bit Linux versions on blender.org:
Is there a reason for using a 32 bit OS? In this day and age, almost all available hardware - even heavily outdated components - should be able to run 64 bit software…
In general you should stay away from repo versions of Blender, as with those you are at the mercy of the repo maintainer, who may or may not know what he/she is doing…
Oh, I thought that on my system a 64 bit OS wouldn’t run. Here’s the Ubuntu system info:
By fall this year, I want to buy a faster PC optimized for 3D rendering because my current PC is very slow.
According to the specs on the Intel webpage the E8400 supports 64 bit: https://ark.intel.com/products/33910/Intel-Core2-Duo-Processor-E8400-6M-Cache-3_00-GHz-1333-MHz-FSB…
You could try it out with a 64 bit Linux “Live” DVD. But let’s see if using official Blender does any good first.
I downloaded & unpacked the tar.bz archive from blender.org. Right now, Cycles is rendering the file, and so far there are no artifacts present 
I’ll see if my brother-in-law can burn a DVD with the 64 bit version of Ubuntu for me.
Here’s the latest render:
