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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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