Mapping a process in a remote server to a oracle session

Something we have probably needed many times is to find in a remote server the program that is running a session against our database.
Perhaps and for any reason,  we need to know exactly which concrete process in the remote server is accessing our database (from the
operating system perspective).
Let's say is a sqlplus prompt, but when we log on the remote system, we see that there are many sqlplus processes runnning. Which
is the right one?

Who And What SQL Is Using Temp Segments ?

Recently I came across an incident related to temporary segments. When I checked the view V$SORT_USAGE to take a look at what was using my temporary tablespace, I got shocked to see a query of the type "select 1 from dual". Obviously, this query does not do any kind of sort!

So I decided to take a close look at the issue.

First thing I noticed:

ORA-00030, 00000, "user session ID does not exist"

I think it's worth to write a short entry in my blog regards to it. That happened to me some days ago. First time I met this issue.

We were told that a session was blocking another session and preventing it to run a DELETE on one table. Up to this point, everything is normal. I ran an ALTER SYSTEM KILL SESSION.. on the blocking session, and, to my surprise, appeared this message: