Find locks (does not always return results – if so, try details query below): select s1.username || '@' || s1.machine || ' ( SID=' || s1.sid || ' ) is blocking ' || s2.username || '@' || s2.machine || ' ( SID=' || s2.sid || ' ) ' as blocking_status from v$lock l1 , v$session s1 , v$lock l2 , v$session s2 where s1.sid = l1.sid and s2.sid = l2.sid and l1.block = 1 and l2.request > 0 and l1.id1 = l2.id1 and l2.id2 = l2.id2
Lock details: select l.inst_id , substr(l.oracle_username,1,8) as ora_user , substr(l.session_id,1,3) as sid , s.serial# , substr(o.owner || '.' || o.object_name,1,40) as object , p.spid as os_pid , decode( l.locked_mode , 0, 'NONE' , 1, 'NULL' , 2, 'ROW SHARE' , 3, 'ROW EXCLUSIVE' , 4, 'SHARE' , 5, 'SHARE ROW EXCLUSIVE' , 6, 'EXCLUSIVE' , null ) as lock_mode , s.lockwait from sys.gv_$locked_object l , dba_objects o , sys.gv_$session s , sys.gv_$process p where l.object_id = o.object_id and l.inst_id = s.inst_id and l.session_id = s.sid and s.inst_id = p.inst_id and s.paddr = p.addr(+) order by l.inst_id

select t.* , s.sid , s.serial# , p.spid os_pid from dba_ddl_locks t , sys.gv_$session s , sys.gv_$process p where t.session_id = s.sid and s.inst_id = p.inst_id and s.paddr = p.addr(+) and t.mode_held <> 'Null' order by 1

Kill Locks (nice): ALTER SYSTEM KILL SESSION 'sid,serial#' IMMEDIATE;
Kill Locks (not so nice), on Linux commandline:

kill -9 OS_PID