SQL> select banner from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE    11.2.0.4.0      Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production

SQL> select sum(bytes) from dba_free_space where tablespace_name='UNDOTBS1';

     SUM(BYTES)
---------------
  9 890 758 656

SQL> select sum(bytes) from dba_data_files where tablespace_name='UNDOTBS1';

     SUM(BYTES)
---------------
 10 464 788 480

SQL> select status,sum(blocks) from dba_undo_extents where tablespace_name='UNDOTBS1' group by status;

STATUS             SUM(BLOCKS)
------------------ -----------
UNEXPIRED              41 256
EXPIRED                25 616

SQL> select count(*) from dba_rollback_segs where status='OFFLINE';

  COUNT(*)
----------
        11

SQL> Show parameter Undo

NAME                                 TYPE     VALUE
------------------------------------ -------- ------------------------------
undo_management                      string   AUTO
undo_retention                       integer  900
undo_tablespace                      string   UNDOTBS1

SQL> select max(tuned_undoretention) from v$undostat;

MAX(TUNED_UNDORETENTION)
------------------------
                    3598


SQL> select TABLESPACE_NAME,AUTOEXTENSIBLE,BYTES,MAXBYTES,substr(FILE_NAME,1,instr(FILE_NAME,'/',2)-1) mounted from dba_data_files where TABLESPACE_NAME='UNDOTBS1';

TABLESPACE AUT           BYTES        MAXBYTES MOUNTED
---------- --- --------------- --------------- -------
UNDOTBS1   YES  10 464 788 480  34 359 721 984 /u02

SQL> host df /u02 -H
Filesystem             Size   Used  Avail Use% Mounted on
/dev/sdb1              1.1T   442G   587G  43% /u02