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Re: Merging / and /usr (was: jessie release goals)

On Wed, May 8, 2013 at 12:52 AM, Marco d'Itri <md@linux.it> wrote:
> On May 07, Jonathan Dowland <jmtd@debian.org> wrote:
>> > If we do this, I'd prefer to make /usr a symlink to / on new installs
>> I've always thought that myself, but it seems most folks who are pro
>> merge tend to propose going the other way. I've never understood why.
> I was trying to not start a new discussion about this, but since you
> asked: moving /usr in / does not solve any significant problem, while
> moving /{bin,sbin,lib} to /usr allows some very interesting new things
> like being able to have a truly shared stateless /usr containing the
> whole OS, which can be used for things like appliances which can then be
> upgraded and rolled back with a single rename(2).
> The Fedora page explains some:
> http://fedoraproject.org/wiki/Features/UsrMove

I support doing /usr move, for it can help on making better use of
snapshot function of BTRFS/ZFS.

An easy example is that, on Solaris, there is a something called boot
environment (BE), which is essentially snapshots of the combination of
/usr and /boot, users can switch between different BEs easily without
affecting any user data. Without /usr merge, doing such work could be
much more complicated because user data and system data is mixed in
the file system's hierarchy, it's hard to make sure switching between
different snapshots won't change user data. While if such thing is
done properly, then user won't be bothered about messing up the system
on upgrades or experiments anymore. They can switch among different
working environments easily, without dealing with the odds caused by

There is apt-btrfs-snapshot around for some time (hasn't been in
Debian, yet), and it can be relied upon in production systems only
when the separation of system data and user data is done.

Aron Xu

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