Re: [gentoo-user] systemd and initramfs

[J. Roeleveld]

On Wed, August 21, 2013 22:02, Neil Bothwick wrote:
> On Wed, 21 Aug 2013 11:50:57 -0400, Tanstaafl wrote:
>
>> > This sounds like a bug in LVM. If it was down to a version clash, why
>> > did a restart find the PVs?
>>
>> Sorry, ianap, but I do know that this kind of thing has never happened
>> to me in my 8+ years of running this old system with a separate /usr
>> *without* an initramfs...
>
> Which proves absolutely nothing. For all we know you don't use LVM either.

True, except that I have been using LVM for that long with a seperate LVM.
My partition scheme used to look like:
1) /boot (100M)
2) /  (500M)
3) swap (whatever seemed logical)
4) LVM (rest)

And then the larger parts in seperate LVs. This always worked for me and I
never had any issues with any programs running on my machines.
As it looks like we are being forced to use an initramfs if /usr is
seperate, I decided to use the following partitioning:
1) /boot (300M)
2) LVM (rest)

And simply put everything into LVM.

>> So, the bottom line is, obviously (to me at least), there are a lot
>> more things that can go wrong when an initramfs is involved, that
>> simply don't or can't happen otherwise.
>
> I'd take issue with "a lot" but there are things that can go wrong with
> an initramfs (but this wasn't one of them, it was PEBKAC) just as there
> are things that can go wrong when you use a separate /usr without an
> initramfs.

I agree with the PEBKAC, but a simple method to identify when the
initramfs is out-of-sync with userland tools would help. Preferably
something integrated into portage that puts out a warning when a package
that has parts in the initramfs is updated mentions that the initramfs is
out-of-sync.

>> >> And this is *precisely* what scares me about this.
>> >>
>> >> This simply should not be, period. Support for separate /usr without
>> >> initramfs simply SHOULD NOT be dropped unless/until things like this
>> >> (updating lvm) can *never* cause a system to fail to boot like
>> >> this.
>
> No one has demonstrated that it can. An initramfs isn't magic, it
> caries out a couple of trivial tasks before switching to the real root
> partition.

The issue mentioned was an example. It was also:
1) The only one I can remember from the last 4 or 5 years
2) Easily avoided with a "rebuild initramfs" notice during upgrade

> Yes, an initramfs adds an extra step to the boot process, but so does
> having a separate /usr in the first place. I think that if you took the
> time to understand what an initramfs is and does instead of making an
> emotional reaction to it, you would see that this is no big deal.

I think part of the "problem" with it is that the documentation about it
isn't clear. There are tools (genkernel / dracut /..? ) that can automate
the generation of it. But it isn't clear what exactly it is doing.
If there would be a clear guide on how to do it manually, or a tool that
would assist in building the file(s) needed to have it build into the
kernel, then it might be more acceptable to some.

I currently use genkernel, simply because it works-for-me and I haven't
had the time to investigate how to get my setup supported with an
in-kernel version.

>> > This is irrelevant to separate /usr. an initramfs is required if / is
>> > on a VM, whether or not /usr is on the same LV.
>>
>> Sorry, I don't see where he said that this system was running on a
>> VM... or did you mean where he had / on an *LVM* partition - which,
>> again, he did not say he had.
>
> Sorry, I meant LV.

The person with the issue did not mention having / on LVM.

I also never had any issues with /usr on LVM while / was not.

--
Joost