Cannot upgrade from Ubuntu 18.10 to 19.10

Question

When running the command sudo do-release upgrade I'm facing the following errors:

Checking package manager
Can not upgrade 
An upgrade from 'cosmic' to 'eoan' is not supported with this tool. 

Answer 1

Since 18.10 no longer supported you can upgrade manually to 19.04

mkdir /tmp/upgrade
cd /tmp/upgrade
wget http://old-releases.ubuntu.com/ubuntu/dists/disco-updates/main/dist-upgrader-all/current/disco.tar.gz
tar -xvf disco.tar.gz
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
/etc/apt/sources.list change all links prefix to -> http://old-releases.ubuntu.com/
sudo python3 dist-upgrade.py

Then upgrade to 19.10

sudo cp /etc/apt/sources.list.bak /etc/apt/sources.list
sudo sed -i -e 's|cosmic|eoan|g' /etc/apt/sources.list
sudo apt update
sudo apt upgrade

Answer 2

I just experienced the whole process of upgrading from 18.10 to 20.04LTS. Key steps are first upgrading from 18.10(cosmic) to 19.04(disco), then 19.10(eoan), finally 20.04LTS(focal).

1. Upgrade from 18.10 to 19.04. First, we have to manually download disco updates:

   mkdir /tmp/upgrade
   cd /tmp/upgrade
   wget http://old-releases.ubuntu.com/ubuntu/dists/disco-updates/main/dist-upgrader-all/current/disco.tar.gz
   tar -xf disco.tar.gz
   

   Now, modify /etc/apt/sources.list(Tip: you'd better save the original sources.list as a backup). This file in Ubuntu 18.10 is like this:

   

   However, "archive.ubuntu.com" has been dead, so we have to replace these links by "old-releases.ubuntu.com", then run dist-upgrade.py in current directory, which is extracted from disco.tar.gz:

   sudo sed -i 's/archive.ubuntu.com/old-releases.ubuntu.com/g' /etc/apt/sources.list
   sudo sed -i 's/cosmic/disco/g' /etc/apt/sources.list  # some answers may forget this
   sudo python3 dist-upgrade.py
   

   Note that if you forget to replace "cosmic" with "disco", when running this script, it may throw this dialogue box:

   

   Don't worry, choose "Yes", just like it said, it will update all "cosmic" to "disco" entries.

   When this script succeeds, reboot your system and now you have Ubuntu 19.04(disco). Your /etc/apt/sources.list should be like this:

   

2. Upgrade from 19.04 to 19.10. Again, replace "disco" to "eoan" in /etc/apt/sources.list. Now you can run apt for updating:

   sudo sed -i 's/cosmic/eoan/g' /etc/apt/sources.list
   sudo apt update
   sudo apt upgrade
   

   If everything goes well, reboot your system and you got 19.10(eoan)! If you just want 19.10, feel free to skip step 3, it's for users who want 20.04 LTS.

3. Upgrade from 19.10 to 20.04 LTS. This is quite easy, just use Ubuntu Software Updater, it will do everything for you. It took me about 2-3 hours to download and install all updates.