Is it possible to attach several DTraces to a single process?

Question

Hi,
Is it possible to attach dtrace to a single process twice or more times? (with different scripts)?
Each time I tried, it fails with the message
"failed to grab pid 13407: process is traced"
I ended up with two simplest scripts
dtrace -n 'END { printf("BYE"); }' -p 13407
dtrace -n 'BEGIN { printf("Hi there"); }' -p 13407
but they failed with the same message.
Does this mean that it is impossible to attach several scripts to a single process?
Or do I misunderstand something?
Thank you,
Vladimir

Answer 1

Hi Vladimir,
The documentation isn't very clear on this, but -p (and -c) "grab" the target process which means they take exclusive control of it like a debugger would. If you instead pass the pid as a script parameter and replace all $target with $1 (or whatever) dtrace doesn't "grab" and you can attach as many things as you want (including a debugger, though it's likely to blow up if you set a breakpoint in a function dtrace has messed with)
Regards,
Ryan