After install openerp on raspberry Pi, and i run openerp-server it shows "OperERP server is running, waiting for connection".

However, when I use client broswer accessing "http://192.168.1.139:8069" it shows "500 Internal Server Error" with the following message,

{"message": "OpenERP Server Error", "code": 200, "data": {"debug": "Server Traceback (most recent call last):\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/session.py\", line 89, in send\n return openerp.netsvc.dispatch_rpc(service_name, method, args)\n File \"/usr/lib/pymodules/python2.7/openerp/netsvc.py\", line 296, in dispatch_rpc\n result = ExportService.getService(service_name).dispatch(method, params)\n File \"/usr/lib/pymodules/python2.7/openerp/service/web_services.py\", line 122, in dispatch\n return fn(*params)\n File \"/usr/lib/pymodules/python2.7/openerp/service/web_services.py\", line 359, in exp_list\n cr = db.cursor()\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 484, in cursor\n return Cursor(self.__pool, self.dbname, serialized=serialized)\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 182, in __init__\n self._cnx = pool.borrow(dsn(dbname))\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 377, in _locked\n return fun(self, *args, **kwargs)\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 440, in borrow\n result = psycopg2.connect(dsn=dsn, connection_factory=PsycoConnection)\n File \"/usr/lib/python2.7/dist-packages/psycopg2/__init__.py\", line 179, in connect\n connection_factory=connection_factory, async=async)\nOperationalError: could not connect to server: No such file or directory\n\tIs the server running locally and accepting\n\tconnections on Unix domain socket \"/var/run/postgresql/.s.PGSQL.5432\"?\n\n\nClient Traceback (most recent call last):\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/http.py\", line 285, in dispatch\n r = method(self, **self.params)\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py\", line 570, in index\n db, redir = db_monodb_redirect(req)\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py\", line 98, in db_monodb_redirect\n return db_redirect(req, not config['list_db'])\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py\", line 109, in db_redirect\n dbs = db_list(req, True)\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/controllers/main.py\", line 90, in db_list\n dbs = proxy.list(force)\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/session.py\", line 30, in proxy_method\n result = self.session.send(self.service_name, method, *args)\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/session.py\", line 103, in send\n raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)\nFault: <Fault could not connect to server: No such file or directory\n\tIs the server running locally and accepting\n\tconnections on Unix domain socket \"/var/run/postgresql/.s.PGSQL.5432\"?\n: 'Traceback (most recent call last):\\n File \"/usr/lib/pymodules/python2.7/openerp/addons/web/session.py\", line 89, in send\\n return openerp.netsvc.dispatch_rpc(service_name, method, args)\\n File \"/usr/lib/pymodules/python2.7/openerp/netsvc.py\", line 296, in dispatch_rpc\\n result = ExportService.getService(service_name).dispatch(method, params)\\n File \"/usr/lib/pymodules/python2.7/openerp/service/web_services.py\", line 122, in dispatch\\n return fn(*params)\\n File \"/usr/lib/pymodules/python2.7/openerp/service/web_services.py\", line 359, in exp_list\\n cr = db.cursor()\\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 484, in cursor\\n return Cursor(self.__pool, self.dbname, serialized=serialized)\\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 182, in __init__\\n self._cnx = pool.borrow(dsn(dbname))\\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 377, in _locked\\n return fun(self, *args, **kwargs)\\n File \"/usr/lib/pymodules/python2.7/openerp/sql_db.py\", line 440, in borrow\\n result = psycopg2.connect(dsn=dsn, connection_factory=PsycoConnection)\\n File \"/usr/lib/python2.7/dist-packages/psycopg2/__init__.py\", line 179, in connect\\n connection_factory=connection_factory, async=async)\\nOperationalError: could not connect to server: No such file or directory\\n\\tIs the server running locally and accepting\\n\\tconnections on Unix domain socket \"/var/run/postgresql/.s.PGSQL.5432\"?\\n\\n'>\n", "fault_code": "could not connect to server: No such file or directory\n\tIs the server running locally and accepting\n\tconnections on Unix domain socket \"/var/run/postgresql/.s.PGSQL.5432\"?\n", "type": "server_exception"}}

I'm a newbie to odoo, I have no concept for everything.  Please help.