Postgresql: Can't access to file « $libdir/postgis-2.1 » no such file or directory
Finally "solve" the issue compiling from source postgis 2.2.2 (that also requires gdal, proj4 and geos) and then issuing
CREATE EXTENSION postgis;
CREATE EXTENSION postgis_topology;
since DROP EXTENSION postgis;
tells me postgis wasn't present anymore.
And finally:
ALTER EXTENSION postgis UPDATE TO '2.2.2';
ALTER EXTENSION postgis_topology UPDATE TO '2.2.2';
Got access again to my geom data and functions from PostgreSQL 9.4. It seems that compiling from source updated correctly the variable path for postgresql and installed /usr/lib/postgresql/9.4/lib/postgis-2.2.so that wasn't present anymore (for postgis-2.1.so as well), even with (re)installing from apt-get.
Hope this will help.
First run (as postgres administrator)
ALTER EXTENSION postgis UPDATE;
If this returns successfully, then check what version you have
SELECT PostGIS_Full_Version();
If however, the server returns that it cannot find the extension postgis, then run
CREATE EXTENSION postgis;
CREATE EXTENSION postgis_topology;
ALTER EXTENSION postgis UPDATE;
and again check by running
SELECT PostGIS_Full_Version();