man useradd ...
-r This flag is used to create a system account. That is, a user
with a UID lower than the value of UID_MIN defined in /etc/login.defs
and whose password does not expire. Note that useradd will not create a
home directory for such an user, regardless of the default setting in
/etc/login.defs. You have to specify -m option if you want a home
directory for a system account to be created. This is an option added
by Red Hat.