How to keep Gnome up to date in a LTS system

[Ralf Mardorf]

There never will be upgrades to another version available. If your LTS
supports GNOME 3.22 it will stay with that version until EOL.

Compare https://packages.ubuntu.com/bionic/gnome and
https://packages.ubuntu.com/eoan/gnome.

Some GNOME components are available by the "main" repository, those
components get updates with security patches.

"Software in main includes a hand-selected list of applications that
the Ubuntu developers, community and users feel are most important, and
that the Ubuntu security and distribution team are willing to support."
- https://help.ubuntu.com/community/Repositories#Main

Other parts of GNOME are provided by the "universe" repository, they
might never get a security upgrade at all.

"Canonical does not provide a guarantee of regular security updates for
software in the universe component, but will provide these where they
are made available by the community." -
https://help.ubuntu.com/community/Repositories#Universe

There might be a third party repositories available that provide
release updates of GNOME, but if you are using those, then your LTS
without any doubts becomes unstable from end to end, since GNOME has
got way to many critical dependencies.

I'm using 16.04 LTS without a desktop environment and I build latest
versions from upstream of software such as e.g. claws-mail or lxpanel
against the libraries provided by the official Ubuntu repositories.
This works without any issues, but to build a newer version of GNOME,
you need to build almost all gtk3 related libraries, often even desktop
themes become incompatible. Doing so would render your LTS useless.