Session login user can not rename. You need to create a another super user, log in as a new super user, and then rename default postgres user using alter.
I want to know if I rename 'postgres' user to 'someuser' retaining it's privileges i.e superuser and other privileges.
Or what if I drop the 'postgres' user and create a new superuser. I tried dropping Postgres user but it says "cannot drop role postgres because it is required by the database system".
So my concern is what happens if I rename it. As far as I can check there's no impact, but in case anyone has faced issues regarding this, please suggest.