Add the citusdata repo's
curl https://install.citusdata.com/community/rpm.sh | sudo bash
review the citus repository
yum list available|grep citus
I'm choosing the pg12 version
sudo yum install -y citus102_12
Check if you have any shared_preload_libraries
grep shared_preload_libraries /var/lib/pgsql/12/data/postgresql.conf
in my case there were no existing settings to worry about, so I used the following simple logic
echo "shared_preload_libraries = 'citus'" | sudo tee -a /var/lib/pgsql/12/data/postgresql.conf
then you need to restart postgres
service postgresql-12 status
service postgresql-12 restart
service postgresql-12 status
note you need a full restart and not a reload
service postgresql-12 reload
and final as the postgres user
postgres=# CREATE EXTENSION IF NOT EXISTS citus;
CREATE EXTENSION