SQLPLUS error:ORA-12504: TNS:listener was not given the SERVICE_NAME in CONNECT_DATA

Question

I downloaded SQLPLUS from Oracle:

http://www.oracle.com/technetwork/topics/winx64soft-089540.html

Basic Lite and SQL*Plus

I then fired up SQL*Plus:

c:\Program Files\Oracle\instantclient_12_1>sqlplus /nolog

SQL*Plus: Release 12.1.0.2.0 Production on Wed Apr 15 15:25:36 2015

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

and tried to connect to a database:

connect user\password@hostname

and received the error message:

ERROR:
ORA-12504: TNS:listener was not given the SERVICE_NAME in CONNECT_DATA

What am I missing?

I ran the queries suggested by Jakub, I got

SQL> select sys_context('USERENV','SERVICE_NAME') from dual;

SYS_CONTEXT('USERENV','SERVICE_NAME')
--------------------------------------------------------------------------------

SYS$USERS

SQL> select sys_context('USERENV','SID') from dual;

SYS_CONTEXT('USERENV','SID')
--------------------------------------------------------------------------------

877

SQL>

Answer 1

You're missing service name:

 SQL> connect username/password@hostname:port/SERVICENAME

EDIT

If you can connect to the database from other computer try running there:

select sys_context('USERENV','SERVICE_NAME') from dual

and

select sys_context('USERENV','SID') from dual