* teach tmpfiles.d q/Q logic something sensible in the context of XFS/ext4
project quota
+* introduce DefaultSlice= or so in system.conf that allows changing where we
+ place our units by default, i.e. change system.slice to something
+ else. Similar, ManagerSlice= should exist so that PID1's own scope unit could
+ be moved somewhere else too. Finally machined and logind should get similar
+ options so that it is possible to move user session scopes and machines to a
+ different slice too by default. Usecase: people who want to put resources on
+ the entire system, with the exception of one specific service. See:
+ https://lists.freedesktop.org/archives/systemd-devel/2018-February/040369.html
+
* maybe rework get_user_creds() to query the user database if $SHELL is used
for root, but only then.