can't install citext extension: could not access file "$libdir/citext": No such file or directory

I'm trying to get citext available as a type in a specific database. The Postgres database server is 9.4. I see it on the server in the pg_catalog's pg_available_extensions view.

From the psql console I try to install it and get this error:

create extension citext;

ERROR:  could not access file "$libdir/citext": No such file or directory

Is there a configuration problem? I'm not sure why it would not have the $libdir variable populated.

Did you perhaps install multiple instances of Postgres on the same server? Standard Postgres is not built for that, $libdir is compiled into the program. If so, you could fix your problem by uninstalling all other instances and and re-installing your current Postgres version.

Related:

• Could not access file “$libdir/plpgsql”: No such file or directory

StackExchange Database Administrators Q#118297, answer score: 2