DTrace not printing aggregations

Question

I'm trying to execute the following very simple use of DTrace from the terminal in OS X 10.8.

sudo dtrace -n 'syscall:::entry { @counts["System Call Entry"] = count(); }'

When I hit ^C I expect the aggregate @counts to be printed out, but instead I just get a blank line printed out. Could someone please tell me why the aggregate isn't being printed?

It's really odd because if I execute the following script, I do see a printout of the aggregation, so the aggregation does have values stored in it.

sudo dtrace -n 'syscall:::entry { @counts[probefunc] = count(); } tick-1sec { printa(@counts); exit(0); }'

score 0 · Answer 1 · answered Feb 12 '13 at 22:43

0

You must leave the probe running a little bit longer for it to set-up and collect some numbers. I found that it takes between 1 and 10 seconds to actually start/collect, only then can you get the aggregate result to print after hitting ^C.

This delay is noticeable on OSX and Solaris, but why it takes a lot longer from time to time I have not been able to determine. [There is a perfectly logical (and unknown) reason of course.]

Also, if you add:

dtrace:::BEGIN { printf("Starting...\n"); }

into your probe, you see the delayed start. However, it then takes a bit more time to collect the first set of numbers. It won't print the "aggregate" until the syscall:::entry probe has fired and accumulated something.

answered Feb 12 '13 at 22:43

PaulS

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Leaving it running for several minutes still didn't produce any results. I think the behaviour might have changed in an OS X release, as I get the ^C print out on Snow Leopard – James Bedford Feb 13 '13 at 11:22
Interesting, I'm using OS X 10.7.5 which works. If you add the "Starting" part (above), does that print? – PaulS Feb 13 '13 at 12:45
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Yea the "Starting..." prints, maybe it's just a 10.8 thing. – James Bedford Feb 13 '13 at 14:03
Seeing the same thing on Mac OS X 10.8. – Sim Jul 19 '13 at 01:24

DTrace not printing aggregations

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