Trying to understand the function/purpose/effectiveness of LTS

[Ralf Mardorf]

PS: Regarding security upgrades also take care about the repository
policy.

"Main

The main component contains applications that are free software, can be
freely redistributed and are fully supported by the Ubuntu team. This
includes the most popular and most reliable open-source applications
available, many of which are included by default when you install
Ubuntu. 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. When you install software from the main component,
you are assured that the software will come with security updates and
that commercial technical support is available from Canonical.

Restricted

Our commitment is to only promote free software – or software available
under a free licence. However, we make exceptions for a small set of
tools and drivers that make it possible to install Ubuntu and its free
applications on everyday hardware. These proprietary drivers are kept
in the restricted component. Please note that it may not be possible to
provide complete support for this software because we are unable to fix
the software ourselves - we can only forward problem reports to the
actual authors. Some software from restricted will be installed on
Ubuntu CDs but is clearly separated to ensure that it is easy to
remove. We will only use non-open-source software when there is no
other way to install Ubuntu. The Ubuntu team works with vendors to
accelerate the open-sourcing of their software to ensure that as much
software as possible is available under a free licence.

Universe

The universe component is a snapshot of the free, open-source, and
Linux world. It houses almost every piece of open-source software, all
built from a range of public sources. 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. Users should understand the risk inherent in using these
packages. Popular or well supported pieces of software will move from
universe into main if they are backed by maintainers willing to meet
the standards set by the Ubuntu team.

Multiverse

The multiverse component contains software that is not free, which
means the licensing requirements of this software do not meet the
Ubuntu main component licence policy. The onus is on you to verify your
rights to use this software and comply with the licensing terms of the
copyright holder. This software is not supported and usually cannot be
fixed or updated. Use it at your own risk." -
https://help.ubuntu.com/community/Repositories