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On my laptop I have Xubuntu 20.04. I've noticed that running # apt update && apt upgrade -y hardly ever results in updates being applied.

Upon doing a comparison of /etc/apt/sources.list between my laptop and a fresh Xubuntu (installed in a VM using the 20.04.1 point release ISO), I've noticed that the following lines are missing (as opposed to commented out) on my laptop's version of the file:

deb http://gb.archive.ubuntu.com/ubuntu/ focal-updates main restricted
deb http://gb.archive.ubuntu.com/ubuntu/ focal-updates universe
deb http://gb.archive.ubuntu.com/ubuntu/ focal-updates multiverse
deb http://gb.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

What could have caused this difference between the two installations and how can I avoid it happening in future?

Edit

  1. It has been proposed to close this question on the basis that this is a duplicate. That question asks how to restore a broken sources.list file. I already know how to do that. My question is asking why the lines are missing the in first place. The two questions are not duplicates of each other. Whilst I am grateful for efforts to locate a duplicate, please be careful to make sure that it actually is before submitting a close-vote.
  2. It was suggested in the comments that I must have edited the file myself. This is not the case. The file sources.list.save is missing exactly the same lines and has a modified date of 26 April 2020 which is the date that I installed the system (a few days after 20.04 was released in case that is significant).
Jon Bentley
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  • Was one install with the "Download updates while installing" flag and or the "Install 3rd party..." flag? And the other install without? – darth_epoxy Sep 21 '20 at 10:15
  • @darth_epoxy The VM definitely was installed *with* that. It's quite possible the laptop was not; I don't remember. Does that impact what appears in sources.list? – Jon Bentley Sep 21 '20 at 10:16
  • @N0rbert No, because my question is not how to restore it, it's why it ended up in that state in the first place (see my final paragraph). I have already restored it by inserting the missing lines manually. – Jon Bentley Sep 21 '20 at 10:19
  • You've ran some command and removed the entries. As simple as that. We can't guess what was that command and where did you find it. – Pilot6 Sep 21 '20 at 11:04
  • @Pilot6 No, I have not done that. Please see item 2 in my edit. – Jon Bentley Sep 21 '20 at 11:10
  • There was no "early faulty ISO". The iso was never changed if this is an official re;aease iso. So this can't be reproduced. – Pilot6 Sep 21 '20 at 11:29
  • @Pilot6 I've removed the "early faulty ISO" wording as this is simply a distraction. My main point remains: my system had a freshly installed state whereby the lines were missing in `sources.list`. The suggestion that it can't be reproduced is an assumption on your part (as was your earlier statement that I must have run a command that altered it). It's quite possible that there is a known set of circumstances which results in this scenario during installation, and that someone who knows will be able to answer. Clearly it *is* possible for it to happen since it did indeed happen to me. – Jon Bentley Sep 21 '20 at 13:06
  • @JonBentley please provide md5sum and/or sha256sum of the installation media and add output of `grep ^deb -r /etc/apt/ --include=*.list` to the question body. – N0rbert Sep 21 '20 at 13:22
  • @N0rbert I will attempt the first (if I still have the installation media) and edit in the second. However regrettably my question has been closed as a duplicate when it is not, so I have had to flag for moderator help. I will update when that is resolved. – Jon Bentley Sep 21 '20 at 13:29

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