Repository can not be authenticated

Solution 1:

As for does a PPA support you release

If I want to add a PPA that a howto, or web.post tells me will work with Ubuntu, some basic steps to follow could be

• go to the PPA main page

eg. https://launchpad.net/~ubuntu-audio-dev/+archive/ubuntu/ppa and read the developers notes. For my example the notes are rather vague. However scrolling down I can see in the "Overview of published Packages" section a list of packages, dates of upload, uploaded by etc. This is your first clue, most dates are 2010-2012, with only a single 2013.

Your release is Ubuntu 16.04, or the Ubuntu release from 2016 April. This is a long time past 2013, so you've detected a problem here.

• go to the PPA download folder (where your machine will go)

eg. http://ppa.launchpad.net/ubuntu-audio-dev/ppa/ubuntu/dists/ I use this myself quite often (as it involves less reading, which is why it was mentioned in the first comment). What you'll see is a list of folders for each supported release. Ubuntu 16.04 is Xenial, so to support xenial there must be a folder for xenial, but there isn't. The latest folder is 'raring' or 13.04, the 2013 upload in the prior section. Problem detected here too.

If this for my own machine, or a box I valued (eg. production)

the main PPA page is a must, as I tend to look there at the way its written, how it's written by (even if I don't know the people, in my example its a team of 90 'active' members which gives a good feeling) and try and see if I trust this source. Here I think the PPA looks good, except it appears old...

As for replacement sources

I can't help here sorry. I don't know why you added the PPA, so I don't know what you are looking for so can't find a replacement.

If however instructions that told you to add this PPA are from an older release, check you actually need it. For example I added a PPA in Ubuntu 14.04 LTS, and 16.04 LTS for Redshift because I found the night color change helpful. Ubuntu 17.10 & 18.04 LTS however don't need it anymore; having the desired function by default.