[How to] Find [Linux] OS user from [Database listed] OS ID?

We are investigating who performed a shutdown the database. Per the alert logs a shutdown immediate was done by OS ID 31676

Shutting down instance (immediate) (OS id: 31676)

I already checked the /etc/passwd for that UID. Is there a way we can find out the OS user from this OS ID?

I also try using it as PID and didn't work.

select b.spid,a.sid, a.serial#,a.username, a.osuser

from v$session a, v$process b

where a.paddr= b.addr

and b.spid='&spid'

order by b.spid;