Use the standard prex list command to list kernel probes and their attributes. For example, to list the name and keys attributes of the probe named pagein:
prex> list name=pagein keys name=pagein keys=vm pageio io
To list the name and keys attributes of all probes in the io group:
prex> list name keys probes io name=biodone keys=io blockio name=physio_start keys=io rawio name=pagein keys=vm pageio io name=pageout keys=vm pageio io name=physio_end keys=io rawio name=strategy keys=io blockio prex>
The next step is to trace and enable the probes you need. For example, to select all probes whose keys specify thread, vm, and io, and prepare them for tracing:
prex> trace thread vm io # attach trace function to probes prex> enable thread vm io # enable probes prex>
Unlike user-level probes, kernel probes are not automatically `traced' (in prex terminology) when prex attaches to the kernel. You must explicitly issue the trace and enable commands as shown above.
At this point the relevant probes are ready for tracing, but kernel tracing has not been globally enabled so no trace records are being written.