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Re: support for merged /usr in Debian



On 01/05/2016 01:17 AM, Adam Borowski wrote:
> On Mon, Jan 04, 2016 at 08:43:02PM +0100, Michael Biebl wrote:
>> Am 04.01.2016 um 19:12 schrieb Eric Valette:
>>>> 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.
>>> As explained elsewhere in this thread, using initramfs is still not
>>> mandatory in debian
>>
>> an initramfs is not mandatory as long as you don't have /usr on a
>> separate partition.
>> No initramfs + split /usr is not supported and has been broken for a while.
> 
> I guess you meant "with systemd".  It does works with any other init system.

It also "works" with systemd (the same as with other init systems),
you can just try it in a VM if you like. (Compile your own kernel,
change your block device driver + your root filesystem driver from
module to compiled-in, have a separate /usr partition and boot an
otherwise default Jessie system with systemd - it will boot and
mount /usr.)

Which binary is run as PID 1 has never been the issue, both sysvinit
and systemd support /usr not being mounted at the beginning. The
problem is that a lot of other things (that have nothing to do with
PID 1) might break (and even do, examples have been provided in this
thread) - and the _only_ reason you associate that with systemd is
that systemd developers chose to add a warning to systemd 5 years ago
in order to put people on the right track if they experience some
really weird problems in their systems (because breakage due to this
can be *very* subtle).

It's not supported in systemd only in the sense that the developers
really don't want to have to spend time helping people debug
problems with other software that in the end turn out to be because
/usr wasn't available early enough.

All this has been explained in this thread multiple times.

Regards,
Christian

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