Focus on achieving your goal, not on fixing the specific tool. If you're trying to kill Chromium's tab processes but not the main process, start by comparing their command lines, e.g. using ps -efww or pgrep -alf chromium.

You'll see that all "child" processes have a parameter like --type=zygote or --type=renderer. Since this directly describes the process' purpose, it will be more reliable than relying on minor differences in the executable name (which has nothing to do it as all Chromium subprocesses are named the same; the fact that "chromium-browser" used to work was just an artifact of Ubuntu's packaging).

Since this is part of the command line, you'll have to use pkill -f to match it:

pkill -f -- "--type=renderer"

pkill -f -- "chromium --type=renderer"

Finally I was able to achieve the desired result by adding --single-process and --no-zygote args at launch (+ --no-sandbox is required with them).

The number of running Chromium processes aren't growing exponentially anymore, but only two instances remain active: one of them is the usual empty tab in the first position, the second is reused correctly by puppeteer.connect({ browserWSEndpoint }).

[...]
  const browser = await puppeteer.launch({
    headless: true,
    args: ['--single-process', '--no-zygote', '--no-sandbox']
  })
  const browserWSEndpoint = await browser.wsEndpoint()
[...]

• --single-process: Runs the renderer and plugins in the same process as the browser [source]

• --no-zygote: Disables the use of a zygote process for forking child processes. Instead, child processes will be forked and exec'd directly. Note that --no-sandbox should also be used together with this flag because the sandbox needs the zygote to work. [source]

From this bug report on Launchpad, there is one suggestion found in the comments.

Henry Wertz (hwertz10) wrote on 2016-11-04:

[...] I have an Acer Chromebook 13 (Tegra K1) which had 14.04 on it; Chromium 52 or 53 worked fine. Went to 16.04 (managing to hold back X so I could keep the nvidia driver...) and chromium blew up as others have reported.

I also found the 14.04 build of (at this point, chromium 53) worked fine after I set "--disable-namespace-sandbox"... I had the "Aw, snap!" but found (per google) that "--disable-namespace-sandbox" fixed it without the ill effects of "--no-sandbox".