How to check active sessions in Oracle

List active user sessions right now — who they are, where they connect from, and what SQL they run. Excludes Oracle background processes.

SELECT s.sid, s.serial#, s.username, s.status, s.machine, s.program,
       s.module, s.osuser, s.last_call_et,
       q.sql_id, SUBSTR(q.sql_text, 1, 80) AS sql_text
FROM   v$session s
LEFT JOIN v$sql q
       ON q.sql_id       = s.sql_id
      AND q.child_number = s.sql_child_number
WHERE  s.type   = 'USER'
AND    s.status = 'ACTIVE'
ORDER BY s.last_call_et DESC;