[lttng-dev] Issues on basic LTTng trace userspace (tutorial)

[Jonathan Rajotte-Julien]

Hi Julien,

On Wed, Mar 24, 2021 at 11:29:04AM +0000, MONTET Julien via lttng-dev wrote:
> Hello the LTTng team !
> 
> I would like, at first, to thank you for your projet and your impressive work !
> 
> For the past few days I have been trying to learn how to use lttng (v2.12).
> 
> I followed the installation on your website for an Ubuntu 20.04.
> [cid:c663399f-0584-43d3-90c5-3aa277ee7020]

Good. So just to validate you used the stable 2.12 PPA as described in this
section [1] ?.

[1] https://lttng.org/docs/v2.12/#doc-ubuntu-ppa

> 
> The steps to get the trace of a Linux kernel and the babel trace are great !
> 
> However, I am stuck for the 'Trace a user application' : https://lttng.org/docs/v2.12/#doc-tracing-your-own-user-application
> Compilation steps are ok, it launches without error but lttng list --userspace  gives me nothing.

When you perform the `lttng list --userspace` command is your user application
running? If not, `lttng list --userspace` can only list running application.

If your application is running, we will need to go a bit further and have some
debug info.

You can at least check if lttng-ust, on the application side, can successfully
communicate with the lttng-sessiond process. For this, you will have to use
LTTNG_UST_DEBUG.

Here's how to us it:

 1) Make sure a lttng-sessiond is present,
 2) Start your application like so:  LTTNG_UST_DEBUG=1 your_application,
 3) Debug messages from lttng-ust should appear on the stderr.

Please use a paste service [2] to share this information with us. 

[2] https://paste.ubuntu.com/

Au plaisir!

-- 
Jonathan Rajotte-Julien
EfficiOS