From Fedora Project Wiki

I needed to enable out of db rasters in postgis. Here is easy way how to do it using systemd dropin configuration.

sudo -i
mkdir -p /etc/systemd/system/postgresql.service.d
echo <<<EOF
EOF > /etc/systemd/system/postgresql.service.d/dropin.conf
systemctl daemon-reload
systemctl restart postgresql

How to load postgis extensions:

psql -d yourdatabase -c "CREATE EXTENSION postgis;"
psql -d yourdatabase -c "CREATE EXTENSION postgis_topology;"
psql -d yourdatabase -c "CREATE EXTENSION postgis_tiger_geocoder;"

Upgrade (could be real prolbem). You should have installed postgis-upgrade (with previous version of .so). It should be compiled against correct version of postgresql. (It is necessary to build postgresql-upgrade-devel )

ALTER EXTENSION postgis UPDATE TO "2.1.8dev";
ALTER EXTENSION postgis_topology UPDATE TO "2.1.8dev";