How to kill all sessions for a given user in oracle

set head off 
spool tmp.tmp 
select 'Alter system kill session '''||sid||','||serial#||''';' 
from v$session where username='USER_TO_KILL_IN_CAPS' ;
spoof off
@tmp.tmp

kill all sessions for a user

set head off 
spool tmp.tmp 
select 'Alter system kill session '''||sid||','||serial#||''';' 
from v$session where username='USER_TO_KILL_IN_CAPS' ;
spoof off
@tmp.tmp