TNS names (!!! how to set-up real host name?):
  $ORA_HOME/NETWORK/ADMIN/tnsnames.ora 

IHORCL =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = ihorcl)
    )
  )

LISTENER_IHORCL =
  (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))