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Author: Didier Kryn
To: dng
Subject: Re: [DNG] running with separate / and /usr
Le 17/01/2023 à 14:34, ael via Dng a écrit :
> On Tue, Jan 17, 2023 at 10:12:23AM +0100, marc wrote:
>> And here is where the "re-invent it poorly" comes in: Linux
>> has shifted some of this work into the initrd or initramfs. My
>> view is that the initramfs is a mess:
>>    - it differs between distributions
>>    - it is brittle to update (a complex build tool is needed)
>>    - it is redundant (needs to copy loads of files around. Maybe
>>        not an issue on the 100TB system you have, but the smartwatch or
>>        smartbulb builder might see it differently)
>>    - configurations are duplicated, hardcoded or non-obvious.
>>    - it is opaque - not easy to look in to with ls.
>>    - its system recovery utilities are deficient
>>    - as are the interactive tools
> This is probably drifting somewhat from the (/,/usr) topic,
> but I have one problem with eliminating initramfs: CPU firmware
> update. I much prefer to avoid initramfs, and always used to
> compile my own kernels with the necessary 'boot' modules installed.
> But then there seems to be no easy way to patch the CPU firmware
> which is needed not least for security: you need to reboot with the
> new firmware runing, and initramfs is the simplest existing way to achieve that.
> I posted much the same comment on this list long ago and had no
> reaction.
> Are people not risking security, not to mention performance and maybe
> bugs if you don't use initramfs or something else to update the firmware?
> What am I missing? Is there a way to update CPU firwmare on the fly?
> ael

    Managing the early init is certainly something you can do. It means
that you keep using Devuan and its package management for all the system
but for the init stage: you do not install the kernel image and the Grub
package; you need to compile both on your own from source.

    The process is the following:

    1) create a filesystem and build a FSH in your future / partition
with all the utilities needed to boot eg Busybox

    2) write a script named /sbin/init which will perform the tasks
explained below

    3) compile your kernel with the drivers you need to mount the root

    4) install your kernel in /boot of your new partition, and the
collection of modules in /lib

    5) chroot into the new partition and perform the steps necessary to
install Grub on the MBR of the disk

    6) install the debootstrap package on your host and use it to
perform the initial installation of Devuan on your target / or just
install the executable in the target, to invoke it later from your new

    The init script must perform a number of task to reach the status
that the Devuan init expects to find:

    mount /proc, /sys and /dev
    execute a hotplugger, eg mdev
    create a mountpoint for your target root partition eg /mnt
    mount your target root partition on /mnt
    mount /mnt/proc, /mnt/sys,  /mnt/dev /mnt/dev/pts with the proper
filesystems (proc, sysfs, devtmpfs, devpts)
    create /run and eventualy some symlinks from /etc to files/dirs in
/run (I don't remember which)
    then enter an interactive session.
    try 'exec switch-root /mnt /usr/sbin/init' . Don't forget "exec"
because only pid1 can switch-root.
    If it fails, it means you or/and I have forgotten something

    When it all works, include the switch-root command into your script.

    You can then complete the installation of your Devuan system - I
think at least apt-get is available at this stage. Install all you need
but the linux-image and Grub packages: these packages *must not be
installed*. You don't need to often update kernel because updates are
mostly bug corrections. Rebuilding the kernel is essentially needed when
changing release. It takes some learning but it is all manageable.

--     Didier