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Re: support for merged /usr in Debian

On 01/04/2016 12:15 PM, Marc Haber wrote:
> On Mon, 04 Jan 2016 12:01:46 +0100, Ansgar Burchardt
>> Remember that / and /usr don't have to reside on the same partition with
>> the usrmerge proposal: they only have to be both available
>> post-initramfs.  The initramfs already takes care to mount /usr (for the
>> systemd case as initscripts needs updates for sysvinit as was said
>> elsewhere).  So no repartitioning should be required on upgrades.
> I'd like to have a positive confirmation that systemd upstream intends
> to continue supporting this scheme and that Debian will also.

Separate partitions mounted in the initramfs? The whole reason for the
UsrMerge is to make a separate /usr filesystem more interesting - see
the things in the proposal itself and what I've reiterated in [1]. And
the systemd developers are actively interested in things such as
stateless systems or sharing /usr in containers etc.

Also, just from a technical perspective: systemd is also designed to
work in containers, where filesystems are often already pre-mounted to
their respective locations. So systemd must already cope with the fact
that when it's started some mounts may already be present. If you
couple that with the idea that the initrd mounts /usr, then it is
trivially true that /usr can be separate, as long as it's already
mounted before systemd is executed. That will hold true even IF systemd
developers decide to drop support for mounting /usr from a running
system. I'm not saying that somebody couldn't break that scenario if
they tried really hard, but from a technical perspective.


[1] https://lists.debian.org/debian-devel/2016/01/msg00106.html

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