Error while installing Nominatim on ubuntu

Using projection SRS 4326 (Latlong)

NOTICE:  table "place" does not exist, skipping
NOTICE:  type "keyvalue" does not exist, skipping
NOTICE:  type "wordscore" does not exist, skipping
NOTICE:  type "stringlanguagetype" does not exist, skipping
NOTICE:  type "keyvaluetype" does not exist, skipping
NOTICE:  function get_connected_ways(pg_catalog.int4[]) does not exist, skipping
Allocating memory for dense node cache
Allocating dense node cache in one big chunk
Out of memory for dense node cache, reduce --cache size
Error occurred, cleaning up
ERROR: Error executing external command: /home/nominatim/Nominatim/osm2pgsql/osm2pgsql -lsc -O 
gazetteer --hstore -C 4664 -P 5432 -d nominatim /home/nominatim/Nominatim/data/europe/andorra-latest.osm.pbf
Symlinks created
WARNING: Unable to access the website at http://nominatim.localhost/
You may want to update settings/local.php with @define('CONST_Website_BaseURL', 'http://[HOST]/[PATH]/');
ERROR: Site 400-nominatim does not exist!

In Browser url(http://localhost/nominatim/) shows like

string(19) "pgsql://@/nominatim" object(DB_Error)#2 (8) { ["error_message_prefix"]=> string(0) "" ["mode"]=> int(1) ["level"]=> int(1024) ["code"]=> int(-25) ["message"]=> string(29) "DB Error: extension not found" ["userinfo"]=> string(55) " [DB Error: extension not found] ** pgsql://@/nominatim" ["backtrace"]=> array(7) { [0]=> array(6) { ["file"]=> string(21) "/usr/share/php/DB.php" ["line"]=> int(966) ["function"]=> string(10) "PEAR_Error" ["class"]=> string(10) "PEAR_Error" ["type"]=> string(2) "->" ["args"]=> array(5) { [0]=> string(29) "DB Error: extension not found" [1]=> int(-25) [2]=> int(1) [3]=> int(1024) ...
...
...
["_default_error_mode"]=> NULL ["_default_error_options"]=> NULL ["_default_error_handler"]=> string(0) "" ["_error_class"]=> string(8) "DB_Error" ["_expected_errors"]=> array(0) { } } ["type"]=> string(2) "->" ["args"]=> array(2) { [0]=> array(9) { ["phptype"]=> string(5) "pgsql" ["dbsyntax"]=> string(5) "pgsql" ["username"]=> string(0) "" ["password"]=> bool(false) ["protocol"]=> string(3) "tcp" ["hostspec"]=> string(0) "" ["port"]=> bool(false) ["socket"]=> bool(false) ["database"]=> string(9) "nominatim" } [1]=> bool(false) } } [5]=> array(6) { ["file"]=> string(36) "/home/nominatim/Nominatim/lib/db.php" ["line"]=> int(7) ["function"]=> string(7) "connect" ["class"]=> string(2) "DB" ["type"]=> string(2) "::" ["args"]=> array(2) { [0]=> string(19) "pgsql://@/nominatim" [1]=> bool(false) } } [6]=> array(4) { ["file"]=> string(44) "/home/nominatim/Nominatim/website/search.php" ["line"]=> int(10) ["function"]=> string(5) "getDB" ["args"]=> array(0) { } } } ["callback"]=> NULL } DB Error: extension not found