export ORACLE_SID=YourSID
sqlplus "/ as sysdba"

ORA-12514: TNS:listener does not currently know of service requested in connect descriptor

 ORA-1251: TNS:LISTENER DOES NOT KNOW OF SID GIVEN IN CONNECT DESCRIPTOR  

SQL*Plus: Release 10.2.0.3.0 - Production on Wed Aug 24 15:07:41 2016

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.

SQL> connect sys/*****@10.10.11.125 as sysdba
ERROR:
ORA-12514: TNS:listener does not currently know of service requested in connect
descriptor

ORA-01251: Unknown File Header Version read for file number %s

ORA-12514: TNS:listener does not currently know of service requested in connect descriptor
 *Cause:  The listener received a request to establish a connection to a
 database or other service. The connect descriptor received by the listener
 specified a service name for a service (usually a database service)
 that either has not yet dynamically registered with the listener or has
 not been statically configured for the listener.  This may be a temporary
 condition such as after the listener has started, but before the database
 instance has registered with the listener.
 *Action:
  - Wait a moment and try to connect a second time.
  - Check which services are currently known by the listener by executing:
    lsnrctl services <listener name>
  - Check that the SERVICE_NAME parameter in the connect descriptor of the
    net service name used specifies a service known by the listener.
  - If an easy connect naming connect identifier was used, check that
    the service name specified is a service known by the listener.
  - Check for an event in the listener.log file.