sqlplus system/system@//localhost:1521/ORACUSTOM

sqlplus

SQL*Plus: Release 11.2.0.1.0 Production on Sat Nov 10 19:35:34 2012

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Enter user-name: system
Enter password:
ERROR:
ORA-12560: TNS:protocol adapter error

sqlplus system/system@//localhost:1521/ORACUSTOM

orcl =
 (DESCRIPTION =
   (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = TCP)(Host = localhost)(Port = 1521))
   )
 (CONNECT_DATA =
   (SERVICE_NAME = oracustom)
 )
)