Looks like there’s a glitch in rt-setup-database when it tries to process ACLs: the upgrade fails when applying the 4.5.1 ACLs:
Processing 4.5.0 Now populating database schema. Processing 4.5.1 Now populating database schema. Now inserting database ACLs.  [Tue Aug 25 02:42:45 2020] [warning]: do "etc/upgrade/4.5.1/acl.Pg" failed, '.' is no longer in @INC; did you mean do "./etc/upgrade/4.5.1/acl.Pg"? at /opt/rt5/sbin/../lib/RT/Handle.pm line 467. (/opt/rt5/sbin/../lib/RT/Handle.pm:467) Couldn't finish 'upgrade' step. ERROR: Couldn't load ACLs:
This happens with the Postgres (Pg) database backend, we’re running Postgres 11 in our environment.
As implied by the error message adding
. to @INC in rt-setup-database solves the problem - the upgrades all process cleanly after that.
(I’m sure there’s a more elegant solution if I took 15 minutes to look at the code but I’m betting the Best Practical team knows where to look better than me and can fix it in 5 minutes or less.)