We don't (and shouldn't I think) look at them when determining the type of the
user, but they should be used during user/group allocation. (For example, an
admin may specify SYS_UID_MIN==200 to allow statically numbered users that are
shared with other systems in the range 1–199.)
It makes little sense to make the boundary between systemd and user guids
configurable. Nevertheless, a completely fixed compile-time define is not
enough in two scenarios:
- the systemd_uid_max boundary has moved over time. The default used to be
500 for a long time. Systems which are upgraded over time might have users
in the wrong range, but changing existing systems is complicated and
expensive (offline disks, backups, remote systems, read-only media, etc.)
- systems are used in a heterogenous enviornment, where some vendors pick
one value and others another.
So let's make this boundary overridable using /etc/login.defs.
Fixes#3855, #10184.
Zbigniew Jędrzejewski-Szmek