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Re: [tracecompass-dev] How To View Live Traces 
On 2016-03-10 01:33 PM, Michael Steppe wrote:

I hope you are able to view the screenshots I add to these messages.


Yep, works fine here! I think the online archive will scrub them though.


  Here
is another which shows an output of loaded kernel modules (which I grep-ed
for 'ltt'):

[image: Inline image 1]

I couldn't get the 2.7.1 Kernel modules to build in CentOS 6.5, so I had to
downgrade to 2.4.4 (which is documented to still support live tracing).
2.4 is *very* old, and not supported any more upstream. What kernel version are you using? If LTTng 2.4 works, then LTTng 2.7 should too, that's strange. You should report it, along with the error logs, to the lttng-dev mailing list.
I am not even sure if Trace Compass supports live tracing on 2.4. I think the protocol changed at some point and it's possible we only support later versions. Bernd could confirm this. 


  I
also downgraded my lttng-tools and lttng-ust to 2.4.4 to stay in line with
the kernel version. I am still unable to Import/view any live traces as
they are running. I even attempted to download a fresh version of Eclipse
Luna CDT which has linuxtools installed already. Even that control view
does not allow me to select the kernel domain.


Are you able to take kernel traces on that machine?
As Bernd mentioned, you need special rights to trace the kernel. A very easy way to test if you have access to kernel tracing is the command "lttng list -k". If it prints the list of kernel events, you are good to go. However it should print an error if you don't have the requirements (user not in the "tracing" group, modules not installed, etc.)
Simply seeing the modules in lsmod doesn't necessarily means your user can trace the kernel.
If you get an error running "lttng list -k", then it's LTTng that is not configured correctly, and Trace Compass only shows the available options. But if the command works, then there might be a bug on the Trace Compass side. Normally these options are greyed out when the user doesn't have access to kernel tracing. 



  Trying to test the UST
domain as you said would still work, I enabled all UST events and clicked
Import and got a "null argument" error. There was no other details provided
about the error.


That is also strange, but could be due to using LTTng 2.4.


  Is there any way I could get a screenshot by screenshot
view of how you are importing live traces? Are you creating sessions AND
channels and then enabling events or just creating sessions and enabling
events?

Thanks for all your help by the way. I'm sure it is frustrating trying to
explain something that you know works. I just haven't had any luck the past
few weeks trying to view live traces graphically (works with babeltrace but
not very "human readable").
No problem, what is frustrating is that it doesn't work for a user, so we want to help make it work! :) 


Cheers,
Alexandre

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