tempdb filled up twice within three weeks. Dump Tran didn't work. Had to reboot the sybase server. How to find out who and what cause it?
What steps I need to do to turn on the audit on tempdb to capture all activities?
You need to monitor tempdb activity regularly,
you can not audit most of the tempdb activities,
identify which process was running when tempdb was full,
break the long running transactions to small one,
if you are using 12.5 or later versions of 12.5 then look at manuals for "Resource Governer" to know how to restrict tempdb usage
In our monitoring script, we also monitor tempdb usage. Whenever usage increase above 70% we get beeped. This way we can login into the system before hand and find the spid causing the problem. You can do the same. It's not foolproof, but it works.