I had the same issue when upgrading from 18.10 to the newest version. In my case the reason was that I had some packages marked as kept back. This is what I did.
$ sudo apt upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
libodbc1
0 to upgrade, 0 to newly install, 0 to remove and 2 not to upgrade.
I simply removed them along with their dependencies:
$ sudo apt remove libodbc1
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
odbcinst odbcinst1debian2
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED
freetds-bin libodbc1
Then the following sequence of commands led me to the successful upgrade:
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo do-release-upgrade
/etc/apt/sources.list.d/
for a 3rd party package fromhttps://z.litestack.com/v1/repo/ubuntu/
. That URL ceased to resolve (superseded by instructions at zerovm.org/download.htm), soapt-get
would always end up tripping over that.sudo rm /etc/apt/sources.list.d/zerovm-precise.list
fixed it for me.