UbuntuStudio image builds have recently begun failing as a result of adding a
grub theme customization to their flavor, which they then try to apply by
running update-grub from their maintainer scripts. This fails with:
Setting up plymouth-theme-ubuntustudio (0.57) ...
update-alternatives: using /usr/share/plymouth/themes/ubuntustudio-logo/ubuntustudio-logo.plymouth to provide /usr/share/plymouth/themes/default.plymouth (default.plymouth) in auto mode
update-alternatives: using /usr/share/plymouth/themes/ubuntustudio-text/ubuntustudio-text.plymouth to provide /usr/share/plymouth/themes/text.plymouth (text.plymouth) in auto mode
update-initramfs: diverted by livecd-rootfs (will be called later)
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).
dpkg: error processing package plymouth-theme-ubuntustudio (--configure):
installed plymouth-theme-ubuntustudio package post-installation script subprocess returned error exit status 1
Packages providing grub themes should be able to call update-grub from their
maintainer scripts, and they should be able to be installed under
livecd-rootfs. It's surprising to me that this hasn't been a problem before
now for any flavors.
We know that grub-probe should not be called as part of an image build, so
just use our standard helper function to divert it before running the chroot
stage and undivert it after.
When the magic-proxy script could not find a valid InRelease file for the
configured timestamp, it would fall back to serving the canonical version
of it. This meant that builds would succeed, even though snap-shotting the
repository failed.
This update makes the script return HTTP 404 when an InRelease by-hash
link for a given combination of mirror, suite and timestamp cannot be
found.
Installing policyrcd-script-zg2 doesn't quite do this because of the way
that live-build installs its own temporary version of policy-rc.d. The
only remotely sensible way I can see to deal with this is to create the
symlink manually.
When the REPO_SNAPSHOT_STAMP variable is set, the auto/build script will attempt
to launch a transparent HTTP proxy on port 8080, and insert an iptables rule to
redirect all outgoing HTTP requests to this proxy.
The proxy, contained in the `magic-proxy` Python script, examines each request
and silently overrides those pointing to InRelease files or files that are
listed in InRelease files. It will instead provide the contents of the requested
file as it was at REPO_SNAPSHOT_STAMP, by downloading the corresponding asset
"by hash".
Don't install gpg or gpg-agent when building buildd images for series
earlier than bionic. (In earlier series, those packages didn't exist
and gnupg was build-essential.)
