systemd rootprefix migration

Title: systemd rootprefix migration
Author: Mike Gilbert <floppym@gentoo.org>
Posted: 2017-07-16
Revision: 2
News-Item-Format: 2.0
Display-If-Installed: >=sys-apps/systemd-234

Starting with the 234 release, Gentoo's sys-apps/systemd package will
be built with rootprefix=/. This means most of the included programs
and system units will be installed under /lib/systemd instead of
/usr/lib/systemd.

This change brings Gentoo into alignment with most other distros which
still maintain a distinction between boot-critical programs in /, and
less critical programs in /usr. This also means that users with a
separate /usr filesystem will have an easier time booting if their
initramfs should become corrupt or fail.

Symlinks are provided for /usr/lib/systemd/systemd and
/usr/lib/systemd/systemd-shutdown to avoid breaking bootloader configs
and to allow the system to be shutdown/rebooted without issue. These
symlinks will likely be removed in the 235 release, so please update
your boot configuration to reference init=/lib/systemd/systemd.

This change will be mostly transparent to typical users. You may notice
that system units move from /usr/lib/systemd/system to
/lib/systemd/system as you upgrade/re-install packages; this is normal.
Units will function properly from both locations.

After upgrading, please run systemctl daemon-reexec ensure that the new
version is executed. Also make sure to regenerate your initramfs if it
includes a copy of systemd (dracut).

If you encounter a problem, please report a bug.