Problem migrating PostGIS

Question

I need to migrate Postgres 9.3 + PostGIS 2.1 to Postgres 10. I'm using CentOS 7.X

Using pg_upgrade it should be quite straightforward, but the problem is PostGIS. Postgres 9.3 has PostGIS 2.1 available, whereas Postgres 10 has PostGis 2.4.4. So I compiled PostGIS 2.4 for Postgres 9.3 and installed it. Then for each database, I've made:

ALTER EXTENSION postgis UPDATE;

In this way, I've migrated to PostGIS 2.4.

But when I run pg_upgrade, I receive this error:

Cannot access the file «$libdir/postgis-2.1»: It doesn't exist the file or the directory.

If I do this:

cd /usr/pgsql-10/lib/
ln -s postgis-2.4.so postgis-2.1.so

It doesn't work either, because if I run pg_ugrade another time:

pg_restore: creating FUNCTION "public.geomfromewkb("bytea")"
pg_restore: [archiver (db)] Error while PROCESSING TOC:
pg_restore: [archiver (db)] Error from TOC entry 547; 1255 90291 FUNCTION geomfromewkb("bytea") ema
pg_restore: [archiver (db)] could not execute query: ERROR:  could not find function "LWGEOMFromWKB" in file "/usr/pgsql-10/lib/postgis-2.1.so"<br>
    Command was: CREATE FUNCTION "public"."geomfromewkb"("bytea") RETURNS "public"."geometry"
     LANGUAGE "c" IMMUTABLE STRICT
     AS '$libdir/postgis-2.1', 'LWGEOMFromWKB';

Why does Postgres 9.3 reference PostGIS 2.1 after migrating to 2.4?

The other option I see is to compile PosGIS 2.1 for Postgres 10.

UPDATE 1

After reading this tip, I've done for each database I've done:

psql mydb -c 'ALTER EXTENSION postgis UPDATE;' psql mydb -c 'ALTER EXTENSION postgis_topology UPDATE;' psql mydb -f /usr/pgsql-9.3/share/contrib/postgis-2.1/uninstall_legacy.sql psql mydb -f /usr/pgsql-9.3/share/contrib/postgis-2.4/legacy.sql with identical results.

SELECT probin, COUNT(*) FROM pg_catalog.pg_proc WHERE probin LIKE '%/postgis%' GROUP BY probin ORDER BY probin;

returns:

       probin        | count 
---------------------+-------
 $libdir/postgis-2.1 |   373

UPDATE 2

This guide explains the internals of PostGIS migration.

Clearly, PostGIS tells it migrates the extension, but doesn't apply the migration script to change the procedures.

Answer 1

The problem is that I forgot to migrate a template database. Thereafter pg_upgrade upgrades successfully.