How to find out of number connections to Oracle

This queries are mostly used at the time of real QA. I rarely use this query, so i had to write down somewhere to refer.

To find out total number of connections to ORACLE
select count(*) from v$session

To find out machine details and number of connections
select machine,count(*) from v$session group by MACHINE

if you dont have previlage to view this table, work with DBA and get it done.