Lubuntu 18.10 was a standard release, which came out in 2018-October (thus 18.10 using the year.month format used by Ubuntu and flavors), with a supported-life of 9 months. The Lubuntu team tested it to upgrade to the next release, or Lubuntu 19.04 (or the 2019-April release).
Lubuntu 19.04 was likewise tested to upgrade to it’s next release, ie. 19.10 (2019-October release). All those releases (18.10, 19.04 & 19.10) are now EOL or end-of-life. Lubuntu 19.10 could upgrade though to Lubuntu 20.04 LTS.
Upgrades are tested and known to work when a release is supported. However after a release goes EOL, the repository will get moved (see https://help.ubuntu.com/community/EOLUpgrades) meaning eventually the tools won’t see the software anymore as it’s no longer where they look. To avoid this the release-upgrade should occur during the supported life of the product, OR very soon after.
What can you do?
Firstly have you changed your software sources so the cosmic (18.10) software can be found, to ensure your system was fully-upgraded? If you’re fully upgraded (18.10/cosmic wise) you’ve more chance of it working, but it still won’t go to 19.04 (it’s EOL) and skipping releases (ie. 18.10 to 20.04) isn’t recommended.
The next alternative is to
- backup all your data & software
- write a Lubuntu 20.04 LTS ISO to media, and install the new system. I’d use Manual Partitioning, selecting your existing partition(s), and ensure you don’t have format ticked.
This is FAR faster and will skip the missed releases. If you don’t format, it’ll note your added packages, wipe system directories, install, add back your additional packages (if available in your new 20.04 release) then ask to reboot. It won’t erase data unless you had ‘format’ checked, but as that’s easily missed, ensure you’ve backed up your data anyway.
In case you missed the EOL upgrades detail, a supported Ubuntu release can be found at
but after EOL, it gets moved to
Also note: There can be country codes for the main archive, eg. as an Aussie, I could be using http://au.archive.ubuntu.com/ , however there are no country codes for old-releases, so the
au. for me would need removing. I’d use the link I provided firstly. I’ve also assumed your architecture is amd64, if you’re using i386 you should return to Lubuntu 18.04 LTS via re-install.