On Tue, 24 Nov 2015 07:52:47 -0500, Stephen Gallagher wrote:
I've upgraded several family members directly from Fedora 21 to
in the last week with no issues whatsoever (of course, I also curate
their repository selection, so they don't end up with incompatible
Aye, there's the rub. It is not just update from an "original"
installation of N-2 to N, it is update from N-2 plus whatever additional
repository packages were installed plus additional non-repository
software and user configuration that you want to upgrade. The starting
condition is quite variable, and may include old versions of applications
because these are familiar to the user or incompatible with more
When system-upgrade fails (if you are lucky, this will be obvious; if
unlucky, it may not be recognized until after the event), the only way
back to the starting condition is a full system restore. Many users will
back up their own data, and, if upgrade ends badly, plan to recover with
a new installation (of N, N-1, or N-2) and necessary software, followed
by restoration of their personal data. This is the most reliable upgrade
strategy: no exposure to problems with old stuff, and it defines how to
get from a well-known initial state to the user's working environment.
In this case it may be impossible to fix an upgrade problem, because
there is no way to reconstruct the original state and verify successful
upgrade is possible.
Of course, these considerations also apply to the single-release upgrade.
The situation just gets worse the farther back one goes. And sometimes
there simply is no upgrade path: the new software is just incompatible
with the old. To use the new system, you must adapt to it. (Remember
the agony voiced by some GNOME2 users when GNOME3 came along?)
Unlike new installation with its well-defined result, system-upgrade
(with dependencies on user configuration and possibly incompatible pieces
of software) necessarily has some vague result. It is undeniably
valuable and extremely convenient, but unavoidably a second-class
facility. We may insist system-upgrade of a newly installed N-1 to N
works, and further insist system-upgrade of a newly installed N-2 to N
works, but this is deceptive. Once a user configures and uses his
system, system-upgrade is unpredictable.
To add my own to Mr. Gallagher's anecdote, my single attempt at "dnf
system-upgrade" from 21 to 23 failed. After upgrade, my userid was not
displayed on the login screen. Login in text mode was possible. After
an hour or two tinkering with gdm configuration, I gave up, did a new
install of 23, and configured it without difficulty. Several times I
have used "dnf system-upgrade" from 22 to 23 without problems.
Conclusion: release-skipping upgrade is more difficult than
single-release upgrade (and probably not worth the effort to fix.)
If anyone would like to investigate the problem I experienced, I am
willing to install a new 21 system and see if I can reproduce the