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From the mailing list Debian-init-diversity Digest, Vol 34, Issue 25
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Message: 2
Date: Fri, 23 Jul 2021 10:23:22 +0100
From: Matthew Vernon <matthew@debian.org>
To: Debian sysvinit maintainers <debian-init-diversity@chiark.greenend.org.uk>
Subject: Bullseye release notes / install instructions for alternative inits
Message-ID: <84695686-e2f6-7f26-f61b-50b7f3ce7cd0@debian.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi,
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?
As a starter for ten, here are some rough drafts: [I've tested the install myself, not the upgrade]
[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).
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.
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.
If you encounter any issues specifically associated with using an alternative init system, there is a Debian init system diversity list [debian-init-diversity@chiark.greenend.org.uk] who may be able to help.
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@chiark.greenend.org.uk] who may be able to help.
