Bullseye release notes / install instructions for alternative inits

[Martin Steigerwald]

Dear Matthew,

Matthew Vernon - 23.07.21, 11:23:22 CEST:
> I recently installed a new laptop using the latest Bullseye installer,
> and it was reasonably straightforward :) I think we at least want
> something in the install instructions on selecting alternative init
> systems, and maybe also in the release notes on how to switch an
> already-installed system?

Whoa! This is spot on as I am currently writing an article about 
alternative init systems for a German Linux publication :)

It will not be specific to one distribution, but after giving an overview 
about the situation in various distributions I will be focusing on 
Devuan and Debian. I like to mention both and also note some of the 
differences, like network-manager package in Devuan still having an init 
script, while you need to install orphan-sysvinit-scripts on Debian.

I think I will use your mail as a link in the article, since you 
explained very well how to use a different init system in Debian.

In case it does not get accepted into the release notes, which I sure 
hope it does, I think it would be good to put this information into an 
article in Debian wiki.

> As a starter for ten, here are some rough drafts:
> [I've tested the install myself, not the upgrade]
> 
> * Install instructions (
> https://www.debian.org/releases/testing/amd64/index )
> 
> [not sure where to put this - as a new section 6.3.11 maybe ?]
> 
> Installing an alternative init system
> 
> Debian uses systemd as its default init system. Other init systems
> (such as sysvinit and OpenRC) are supported, and the easiest time to
> select an alternative init system is during the installation process.
> 
> The best time to perform the switch is after the "Selecting and
> installing software" stage [link to 6.3.6.2]; though note that the
> default GNOME desktop environment will only work with systemd - so if
> you want a desktop environment installed, then deselect GNOME and
> select another (Xfce, for example, works well without systemd).

GNOME does not work at all? I thought it would be working in Devuan, but 
maybe I am mistaken.

I also know that KDE Plasma works just fine. No matter whether on X11 or 
Wayland. Also Pulseaudio works.

Which other desktops are known to work? XFCE is for sure, it is the 
standard desktop in Devuan. Did anyone test any other?

> Once that stage is complete, launch a shell (see 6.3.9.2. Using the
> Shell and Viewing the Logs), and chroot into the installed system by
> typing `chroot /target`. You then need to tell `apt` to install your
> preferred init system and, unless you are not using a desktop
> environment at all, libpam-elogind to provide the necessary `elogind`
> session management facilities (which are provided by libpam-systemd
> and systemd in a default installation). For example, for
> System-V-like init, type `apt-get install sysvinit-core
> libpam-elogind`. This will install your new init system and elogind,
> and remove systemd, libpam-systemd and other components that can only
> work with systemd. If `apt` is proposing to remove a very large
> number of packages, then you probably selected a desktop environment
> that depends on systemd; it will be best to stop at this point and go
> back to the task selector to chose another instead.

The package "libpam-elogind-compat" from Debian experimental repository 
is no longer necessary? I think I still have it installed on my one 
Debian Sid installation – all other systems are Devuan by now.

In case it is no longer necessary it may be a good idea to remove it 
from Debian experimental repository.

> Once that is done, exit the chroot by typing `exit`, then switch back
> to the installer (if you were using a different virtual console by
> switching back; if you had selected the "Execute a shell" menu
> option, then by typing `exit` once more), and resume the installation
> by moving to the boot loader installation stage, which is typically
> installing GRUB (see 6.3.7. Making Your System Bootable). You can now
> complete the installation process as normal.

Great. It is a very good idea to do it in the installation process 
already.

Also good to mention:

> If you encounter any issues specifically associated with using an
> alternative init system, there is a Debian init system diversity list
> [debian-init-diversity at chiark.greenend.org.uk] who may be able to
> help.

> * Release notes (
> https://www.debian.org/releases/testing/amd64/release-notes/index )
> 
> I think this is a new section under "5.2. Items not limited to the
> upgrade process"
> 
> Switching init system
> 
> The default init system in Debian is systemd. In bullseye, a number of
> alternative init systems are supported (such as System-V-style init
> and OpenRC). Generally, to switch between init systems, you install
> the new init system and reboot. The exception is switching away from
> systemd - systemd's packages will refuse to be removed if systemd is
> running; so the process is a little more involved.
> 
> In outline, you need to download the new packages you need, switch to
> single-user mode, install these new packages, and then reboot. The
> recommended approach is as follows. First, clear out
> `/var/cache/apt/archives` by running `apt-get clean` (this makes
> identifying the packages to install later easier). Next, get `apt` to
> download the new packages you need, e.g.: `apt-get --download-only
> install sysvinit-core libpam-elogind`; libpam-elogind (and elogind
> which it Depends upon) provide session management facilities, which
> you will likely need on any system running a desktop environment. At
> this point, review apt's proposed actions, and if happy, let it carry
> on.
> 
> Now switch to single-user mode (`systemctl rescue`) and install the
> packages you downloaded using `dpkg -i`; the packages will be in
> `/var/cache/apt/archives`. Once dpkg has completed, reboot your
> system.
> 
> If you encounter any issues specifically associated with using an
> alternative init system, there is a Debian init system diversity list
> [debian-init-diversity at chiark.greenend.org.uk] who may be able to
> help.

I think this is a good approach. I am not sure how well this fares with 
a desktop environment already installed.

I remember that at one time apt basically uninstalled my KDE Plasma 
desktop and I had to re-install it again after a switch. But this has 
been a long time ago.

Best,
-- 
Martin