fedora-minimal fails to build on Ubuntu Trusty due do being unable to
find the initrd (see Id4c04d7ae20068643df34d2fa31068e8a917a52d).
This is a rather obscure problem that comes from the intersection of
several things.
The first thing to note is that the post-install scripts of the
kernel-core package use kernel-install [1]. For whatever reason, this
installs the kernel to /boot/MACHINE-ID/KERNEL-VERSION
MACHINE-ID comes from /etc/machine-id; a UUID that should have been
created by the systemd post-inst scripts with systemd-machine-id-setup
[2].
The chroot environment provided for root.d elements has no kernel
file-systems like /proc or /dev mounted. This is where differences in
the base-system come into play -- on more recent systems that
implement getrandom() systemd does not need /dev/urandom to generate
the machine-id [3]; we get a value and /etc/machine-id is populated.
On older platforms (Trusty), systemd-machine-id-setup fails (unable to
access /dev/urandom) and we end up with a blank /etc/machine-id. This
ends up making kernel-install (the script) fail during yum's
installation of kernel-core, which means the initrd is not installed
correctly.
We end up bailing out in fedora-minimal/install.d/99-ramdisk, where we
try to put the installed ramdisk in /boot for the later grub install
scripts to find.
The solution here is to mount the standard kernel file-systems within
the chroot before we try installing.
[1] http://www.freedesktop.org/software/systemd/man/kernel-install.html
[2] http://www.freedesktop.org/software/systemd/man/systemd-machine-id-setup.html
[3] https://github.com/systemd/systemd/blob/master/src/basic/random-util.c
Change-Id: Ibcce35da928f64e6a719b070bcc833346ee7ee92
f307bb4d8b