PostGIS: function ST_AsRaster does not exist. Even using examples from the docs

I'm trying to convert geometries to images, and the functions to do so don't seem to exist.

The following example is from the ST_AsRaster Docs WHich specify the requirements are Availability: 2.0.0 - requires GDAL >= 1.6.0.

SELECT ST_AsPNG(ST_AsRaster(ST_Buffer(ST_Point(1,5),10),150, 150));

This results in:

ERROR: function st_asraster(geometry, integer, integer) does not exist

LINE 1: SELECT ST_AsPNG(ST_AsRaster(ST_Buffer(ST_Point(1,5),10),150,...

I found some info that points towards needing GDAL drivers, however, when I try:

SELECT short_name, long_name FROM ST_GdalDrivers();

I get:

ERROR: function st_gdaldrivers() does not exist

LINE 1: SELECT short_name, long_name FROM ST_GdalDrivers();

I have no idea where to even go to try solving this, why don't the functions exist, was there some config I needed to add, some doc I didn't read?

Even the https://postgis.net/docs/RT_reference.html seems to suggest that it should "just work"?

This is installed from the package manager on Ubuntu 20.0.4.

Version Info SELECT PostGIS_Full_Version();:

POSTGIS="3.0.0 r17983" [EXTENSION] 
PGSQL="120" 
GEOS="3.8.0-CAPI-1.13.1 " 
PROJ="6.3.1" 
LIBXML="2.9.4" 
LIBJSON="0.13.1" 
LIBPROTOBUF="1.3.3" 
WAGYU="0.4.3 (Internal)"

Solution

You must have forgotten to install the postgis_raster extension:

CREATE EXTENSION postgis_raster;

This extension is new in PostGIS 3.0; before that, its objects were part of the postgis extension.

The documentation mentions that:

Once postgis is installed, it needs to be enabled in each individual database you want to use it in.
psql -d yourdatabase -c "CREATE EXTENSION postgis;"

-- if you built with raster support and want to install it --
psql -d yourdatabase -c "CREATE EXTENSION postgis_raster;"