http://www.dba-oracle.com/t_v$session_user_connections.htm

oracle_session.sql

rem session.sql - displays all connected sessions
set echo off;
set termout on;
set linesize 80;
set pagesize 60;
set newpage 0;
 
select
rpad(c.name||':',11)||rpad(' current logons='||
(to_number(b.sessions_current)),20)||'cumulative logons='||
rpad(substr(a.value,1,10),10)||'highwater mark='||
b.sessions_highwater Information
from
v$sysstat a,
v$license b,
v$database c
where
a.name = 'logons cumulative'
;
 
ttitle "dbname Database|UNIX/Oracle Sessions";
 
set heading off;
select 'Sessions on database '||substr(name,1,8) from v$database;
set heading on;
select
substr(a.spid,1,9) pid,
substr(b.sid,1,5) sid,
substr(b.serial#,1,5) ser#,
substr(b.machine,1,6) box,
substr(b.username,1,10) username,
-- b.server,
substr(b.osuser,1,8) os_user,
substr(b.program,1,30) program
from v$session b, v$process a
where
--see code depot for full script
b.paddr = a.addr
and type='USER'
order by spid;
ttitle off;
set heading off;
select 'To kill, enter SQLPLUS> ALTER SYSTEM KILL SESSION',
''''||'SID, SER#'||''''||';' from dual;
spool off;