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

[Jonathan Rajotte-Julien]

Hi Julien,

Please always keep the mailing list in CC.

> I am running 'lttng list --userspace' with the application running in another terminal (like the tutorial, and also with a while that loop on tracepoint(...).

ok.

> 
> You can find here the Ubuntu paste : Ubuntu Pastebin<https://paste.ubuntu.com/p/bWw25kmSTq/>

Based on this, it seems like lttng-ust is unable to find the socket for a sessiond either
locally (for your user) [1] or a global one (root lttng-sessiond) [2].

[1] 43:  libust[207688/207690]: Info: sessiond not accepting connections to local apps socket (in ust_listener_thread() at lttng-ust-comm.c:1822)
[2] 45:  libust[207688/207689]: Info: sessiond not accepting connections to global apps socket (in ust_listener_thread() at lttng-ust-comm.c:1822)

Since you installed via the PPA, a systemd service control service is installed
that control a global (root) lttng-sessiond.

First let's stop it.
   sudo systemctl stop lttng-sessiond.service

Then in a console, again use a paste service to share the content of /tmp/lttng-sessiond.log with us

   sudo lttng-sessiond -vvv > /tmp/lttng-sessiond.log 2>&1

In another console, while the lttng-sessiond process is running, please have a look at the /var/run/lttng directory:

 ls -la /var/run/lttng/

Again use a paste service to share this with us.

Also can you provide the output of the following while using the user you are
normally using to play with lttng:

 groups

You can also try to spawn a local lttng-sessiond for the user.
  Note that a global and many local lttng-sessiond can coexist but for the sake of debugging
  we will only have one of each at a time. 

Kill the root lttng-sessiond we started earlier and start a local one:

 lttng-sessiond -vvv > /tmp/lttng-sessiond-local.log 2>&1 

 Note the absence of `sudo` here.

Again please share the content of /tmp/lttng-sessiond-local.log via a paste
service.

>From there you can retry your experiment with the `lttng list` command.

Cheers


> The command lines entered to compile are quite the same, I just had to modify :
> this :     gcc -o hello hello.o hello-tp.o
> to this : gcc -o hello hello.o hello-tp.o -L/usr/local/lib -llttng-ust -ldl

As per the doc [3]:
    gcc -o hello hello.o hello-tp.o -llttng-ust -ldl

[3] https://lttng.org/docs/v2.12/#doc-tracing-your-own-user-application Bullet point #6

Cheers