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

[Jonathan Rajotte-Julien]

On Wed, Mar 24, 2021 at 03:53:14PM +0000, MONTET Julien wrote:
> Hi Jonathan,
> 
> After having written 'sudo systemctl stop lttng-sessiond.service', the command 'sudo lttng-sessiond -vvv > /tmp/lttng-sessiond.log 2>&1' gives me nothing.


The log should be in /tmp/lttng-sessiond.log.

> 
> ls -la /var/run/lttng/ : Ubuntu Pastebin<https://paste.ubuntu.com/p/gjbqKkCrZK/>
> groups : Ubuntu Pastebin<https://paste.ubuntu.com/p/pjVFHk7kFZ/>
> lttng-sessiond -vvv > /tmp/lttng-sessiond-local.log 2>&1 : nothing
> /tmp/lttng-sessiond-local.log : Ubuntu Pastebin<https://paste.ubuntu.com/p/bj38FhhVpc/>

Based on the log there is a sessiond already running... anyway this give us the
info we need to know for what socket is made available:

application socket path:       /home/montetju/.lttng/lttng-ust-sock-8
wait shm path:                 /lttng-ust-wait-8-1000

Could you share the content of:

   ls -la /dev/shm


TBH nothing points toward a problem here. I would need to spawn a 20.04 to check
if something is broken, I might have time later today.

Cheers

> 
> The issue persist with the 'lttng list' command.
> 
> Best regards,
> 
> Sorry it was indeed :
> The command lines entered to compile are quite the same, I just had to modify :
> > this :     gcc -o hello hello.o hello-tp.o -llttng-ust -ldl
> > to this : gcc -o hello hello.o hello-tp.o -L/usr/local/lib -llttng-ust -ldl
> (I just wanted to focus the importance of  -L/usr/local/lib)
> 
> ________________________________
> De : Jonathan Rajotte-Julien <jonathan.rajotte-julien at efficios.com>
> Envoyé : mercredi 24 mars 2021 16:32
> À : MONTET Julien <julien.montet at reseau.eseo.fr>
> Cc : lttng-dev <lttng-dev at lists.lttng.org>
> Objet : Re: [lttng-dev] Issues on basic LTTng trace userspace (tutorial)
> 
> 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

-- 
Jonathan Rajotte-Julien
EfficiOS