Re: Not capturing ust events

[Kienan Stewart via lttng-dev <lttng-dev@lists.lttng.org>]

Hi David,


On 5/8/25 1:02 PM, David Aldrich wrote:
> Hi Kienan
> 
> Thanks very much for your reply. I can now capture UST events. (My
> actual problem was that I was not linking to lttng-ust).
> 

Glad you caught that. I had assumed it was linked in :)

> I am now using the method you described:
> 
>> lttng create my_proj
>> lttng enable-event --userspace 'lttng_ust_tracef:*'
>> lttng start
>> ./my_app
>> lttng stop
>> lttng view # [Optional]
> 
> This works and captures UST events but I am not capturing Kernel
> events.  My reason for running this experiment is that occasionally
> our application shows glitches where a task takes longer than
> expected. So I want to see what happens in that occurrence - perhaps
> an ISR is running or something like that. So I assume that I need to
> capture Kernel and UST events.
> 
> Can you please advise me why Kernel events aren't being captured?
> 

In the setup above, only a userspace channel is created.

Assuming the user you are running the `lttng` commands with is a member 
of the tracing group and a root lttng-sessiond is running, a complete 
example might look like:

```
lttng create my_proj
lttng enable-event --userspace 'lttng_ust_tracef:*' # this will 
automatically create a channel if one doesn't exist in the session
lttng enable-channel --kernel --session my_proj kernel_channel # [1]
lttng enable-event --kernel --all --channel kernel_channel --session 
my_proj # [2]
lttng start
./my_app
lttng stop
lttng view
```

> Best regards
> David

thanks,
kienan

[1]: https://lttng.org/man/1/lttng-enable-channel/v2.13/
[2]: https://lttng.org/man/1/lttng-enable-event/v2.13/