Snapshotting for rollback after updates was[ Re: Drawing lessons from fatal SELinux bug #1054350]

Chris Murphy lists at
Sun Jan 26 20:30:40 UTC 2014

On Jan 26, 2014, at 12:51 PM, Reindl Harald <h.reindl at> wrote:

> Am 26.01.2014 20:45, schrieb Chris Murphy:
>>> So ?
>>> It is only visible if you downgrade which a lot of software do not
>>> support and explicitly so
>> The right way to do file format changes is you design the new format. 
>> And in a minor version update, the application gains the ability to 
>> read the new file format, but still writes the old file format. 
>> The major version upgrade of the application is enabled to write the 
>> new file format, while it can read either old or new formats.
> please look at the hidden folders in your userhome and /var/lib/
> to get a picture about what we are talking here

This sounds like FUD and there's no actual real world example. You're suggesting that if I have gnome-shell 3.10.3 and I either yum downgrade to 3.10.1, or I do a clean install of Fedora 20 and get gnome-shell 3.10.0, that I'm going to see explosions? What's going to happen? Surely there aren't such significant configuration format changes between such minor versions, and surely the development teams anticipate this very use case where uses have a /home with such files, and have no choice but to revert to an older system with the same major version but lower minor version.

This is why changing configuration formats is hopefully a conscientious decision and not done willy nilly. From many years of experience I know I can reliably upgrade and downgrade at will, within minor versions of OS X - that is all versions of 10.7.x configuration file wise are expected to be compatible. And I'd exclude disposable cache files which by default aren't even backed up anyway as they're expected to be rebuilt on a restore.

Chris Murphy

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