[lttng-dev] snapshot issue in lttng 2.3.0

[Thibault, Daniel]

Date: Tue, 24 Sep 2013 13:42:44 -0700 (PDT)
From: Thuya Aung <thuyaaung2002 at yahoo.com>

> With lttng 2.3.0 in Ubuntu 12.04 LTS, I only get the tracepoints in kernel folder with snapshot mode. I do not see anything for userspace tracepoints. 
> The following is the way I setup for lttng session
>
> lttng create mySession --snapshot
> lttng enable-channel kCh --buffers-global --subbuf-size=1048576 -k
> lttng enable-event -a -k
> lttng enable-channel uCh --buffers-uid --subbuf-size=1048576 -u
> lttng enable-event -a -u
> sleep 1
> lttng start mySession
> sleep 60
> lttng snapshot record
> lttng stop mySession
> lttng destroy mySession
>
> I got the error message saying "Undefined command" with the following
>
> lttng add-output -n myNewOutput file:///home/taung/output (<--- following the examples of man 1 lttng)
>
> Did I do something wrong? What else I should be doing in order to use snapshot feature?
>
> Thuya Aung

   I can confirm this problem (I ran my usual user-space event generator and got nothing for UST in the snapshot).  Regarding your script, there is one mistake made twice: when you enable-event, you need to specify the channel.  You should have gotten an error ("Error: Events: Non-default channel exists within session").  The correct script lines are:

lttng enable-event -a -k -c kCh
lttng enable-event -a -u -c uCh

   As for the output, the mistake is simple.  The correct line is:

lttng snapshot add-output -n myNewOutput file:///home/taung/output

   add-output is a snapshot action, not an lttng command.  Additionally, because a snapshot output is created by default, you must delete it first (currently there is just one output slot):

lttng snapshot del-output 1
lttng snapshot add-output -n myNewOutput file:///home/taung/output

Daniel U. Thibault
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