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Re: support for merged /usr in Debian

On Mon, 4 Jan 2016 13:51:48 +0100, Christian Seiler
<christian@iwakd.de> wrote:
>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].

Actually, having /usr mounted earlier increases the possibility of
something going wrong in early boot. This is good, since early boot is
the only part of Debian's boot process that still is reasonably
debuggable, but that will go away as well as soon as we have systemd
inside the initramfs as well, which will undoubtedly come sooner or
later. Debugging late system boot with the method one has been used to
for decades has already become considerably harder. Thankfully doing
so has not been necessary yet, which might be caused by the solid work
of the systemd people in Debian, who cannot be blamed for the
premature, Ubuntu-like freeze of jessie.

I am just afraid that initramfs' functionality will dramatically
change when systemd takes over initramfs as well, with a lot of
important functionality maked as "broken", "obsolete" and eventually
removed, just as the keyscript= feature of /etc/crypttab was lost a
year ago (noone cared).

The loss of keyscript just broke my clients. I am really afraid of the
first system update breaking my _servers_, causing a resinstall to be
necessary. I know of one customer who already said that if a reinstall
will become necessary, the reinstalled distribution will be called Red
Hat Enterprise Linux. I'd like to postpone this as long as possible.

>the systemd developers are actively interested in things such as
>stateless systems or sharing /usr in containers etc.

Too bad that they have so little interest in the things that are
important to me. I still have to go through painful contortions to
have basic IPv6 functionality and configurability.

>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.

What I am missing is a clearly worded commitment from upstream or
Debian not to break existing systems during upgrades.

-------------------------------------- !! No courtesy copies, please !! -----
Marc Haber         |   " Questions are the         | Mailadresse im Header
Mannheim, Germany  |     Beginning of Wisdom "     | http://www.zugschlus.de/
Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 621 72739834

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