Bug#1114860: systemd: Confusing error message about missing "/etc/machine-id" upon setup

[Josh Triplett]

On Thu, 11 Sep 2025 21:23:00 +0100 Luca Boccassi <bluca at debian.org> wrote:
> On Wed, 10 Sep 2025 22:38:50 +0200 Hilmar Preusse <hille42 at web.de>
> wrote:
> > recently I noticed that setting up systemd failed to setup in one of
> my
> > chroots. The error message was:
> > 
> > <snip>
> > root at rasppi3:~# apt build-dep texlive-bin
> > Summary:
> >   Upgrading: 0, Installing: 0, Removing: 0, Not Upgrading: 0
> >   4 not fully installed or removed.
> >   Space needed: 0 B / 58.3 GB available
> > 
> > Continue? [Y/n] y
> > Error: Can not write log (Is /dev/pts mounted?) - posix_openpt (19:
> No such device)
> > Setting up systemd (258~rc4-1) ...
> > Cannot open '/etc/machine-id' in neither writable nor read-only mode:
> Function not implemented
> > dpkg: error processing package systemd (--configure):
> >  installed systemd package post-installation script subprocess
> returned error exit status 1
> > Errors were encountered while processing:
> >  systemd
> > Error: Sub-process /usr/libexec/apt-eatmydata/dpkg returned an error
> code (1)
> > Error: Failed to process build dependencies
> > <snip>
> > 
> > The root cause turned out to be a not mounted /proc filesystem, the
> setup
> > worked fine after it was mounted. However I found that error message
> quite
> > confusing: the file /etc/machine-id is there and is readable.
> 
> It's accurate, but not helpful, as the file can't be read as file
> descriptors can't be used without procfs. This is not a supported
> setup, sadly procfs is a hard runtime requirement.

Nobody is claiming that this should work without procfs mounted. The bug
report here is about a confusing error message. It would be helpful if
something in this error message mentioned /proc and led the user to
realize it wasn't mounted.