Use below script to find active sessions in oracle database.

set echo off
set linesize 95
set head on
set feedback on
col sid head "Sid" form 9999 trunc
col serial# form 99999 trunc head "Ser#"
col username form a8 trunc
col osuser form a7 trunc
col machine form a20 trunc head "Client|Machine"
col program form a15 trunc head "Client|Program"
col login form a11
col "last call"  form 9999999 trunc head "Last Call|In Secs"
col status form a6 trunc
select sid,serial#,substr(username,1,10) username,substr(osuser,1,10) osuser,
	 substr(program||module,1,15) program,substr(machine,1,22) machine,
	 to_char(logon_time,'ddMon hh24:mi') login,
	 last_call_et "last call",status
from v$session where status='ACTIVE'
order by 1
/