Since 18.04 LTS, Ubuntu has stopped providing installers for the 32-bit variant. Can I install 16.04 LTS, then upgrade it to 18.04 LTS instead?
I assume the correct command would be:
sudo do-release-upgrade
What will happen if I have unity-greeter installed before the upgrade? Supposedly I should end with the 18.04 version of it, but Ubuntu has discontinued Unity in 18.04. (I did actually use Lubuntu with Unity greeter). Or the whole ubuntu-desktop for that matter?
Lubuntu and the other Ubuntu community flavours provide both 64-bit and 32-bit iso files.
You can find the iso files and corresponding checksums via this link
See also the following link,
You've asked a number of questions ...
Some flavors still have 32-bit ISO's (eg. Lubuntu 18.04 LTS has)
Unity is no longer supported by Canonical for 18.04 LTS (but still is for 14.04 LTS & 16.04 LTS) and has moved to 'universe' or now in the community-supported repository. Hence Unity will still work on 18.04 in the same way LXDE, MATE, XFCE does.
ubuntu-desktop in 18.04 means GNOME & no longer Unity, with the Unity DEsktop found in the ubuntu-unity-desktop package in 18.04 LTS
