On Sat, Sep 21, 2024 at 12:41:11PM +0200, Didier Kryn wrote:
> Le 20/09/2024 à 22:56, Ralph Ronnquist via Dng a écrit :
> > On Fri, Sep 20, 2024 at 08:08:08AM -0700, Marc Shapiro via Dng wrote:
> > > Several years ago I was trying to premount a separate partition for
> > > /lib/modules.  I have multiple releases bootable on the system and I wanted
> > > a single place to store the modules, since they can take up a lot of disk
> > > space.
> > >
> > > I tried everything that I could think of, or find online, but nothing
> > > worked.  I gave up on it, then, all of a sudden, it was premounting!  The
> > > odd thing is that it is NOT being done the same as /usr (in
> > > /usr/share/initramfs-tools/init). In fact, since I had given up on it there
> > > is NO entry for it at all in /etc/fstab!
> > >
> > > It has been this was since Daedalus, maybe since Chimaera, and is still
> > > premounting without an /etc/fstab entry in Excalibur (although it is on
> > > /usr/lib/modules in Excalibur).
> > >
> > > Does anyone have any idea how this could be happening? I'm not complaining,
> > > since it was what I originally wanted to do, but I would like to know HOW it
> > > is happening. Even / has to have an entry in fstab. How can this be mounting
> > > without an entry?
> > It's not hard to have rootfs /lib/modules mounted by initramfs init
> > scripting or (post-pivot) startup scripting; the initramfs
> > /lib/modules only needs to include modules to access the rootfs
> > drive(s). Though I can't say how it's done on your system.
> >
>     Premounting is done during initramfs init. The fstab is not available at
> that time.
>
>     One way is getting rid of Debian's initramfs and write your own. This
> way you premount everything you want where you want. I recommend doing like
> Debian for /run and /var/tmp: mount them on tmpfs. I think in this case you
> need to get rid of the kernel packages and build your own kernel, wrapped in
> some way with your initramfs. Alternatively you may boot into a dedicated
> partition instead of initramfs and then switsh_root to the Debian rootfs.
> You keep Debian for userspace only. It just takes a lot of work.

Well, the "normal" initramfs-tools picks up custom scripting from
/etc/initramfs-tools/scripts so you can easily inject something there.
For example, an init-bottom/ script, which is invoked after that the
to-be root filesystem $[rootmnt} is mounted but before switch_root,
can add mounts below that (and it may even read the
${rootmnt}/etc/fstab as a guide, if it needs to be somewhat generic).
If that mounting needs modules then those would best be in the
initramfs /lib/modules tree.

It's all sh scripting; very open and transparent. The actual /init is
found as /usr/share/initramfs-tools/init.

Ralph.

>
> --     Didier
>

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