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

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

[MONTET Julien via lttng-dev]

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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]

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.
I tried of course to add -L/usr/local/lib and -Wl,-rpath,/usr/local/lib

[cid:f913a7d9-4040-468e-ac5d-bea22d81da83]

Have you ever had those kind of issues ?
Could you advise me some debugging methods or solutions ?

Have a nice day,

Julien Montet


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

[Jonathan Rajotte-Julien via lttng-dev]

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

[Jonathan Rajotte-Julien via lttng-dev]

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

[MONTET Julien via lttng-dev]

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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.

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/>

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@efficios.com>
Envoyé : mercredi 24 mars 2021 16:32
À : MONTET Julien <julien.montet@reseau.eseo.fr>
Cc : lttng-dev <lttng-dev@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

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

[Jonathan Rajotte-Julien via lttng-dev]

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@efficios.com>
> Envoyé : mercredi 24 mars 2021 16:32
> À : MONTET Julien <julien.montet@reseau.eseo.fr>
> Cc : lttng-dev <lttng-dev@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
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Re: [lttng-dev] Issues on basic LTTng trace userspace (tutorial)

[Jonathan Rajotte-Julien via lttng-dev]

Hi Julien,

> 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.

Finally I had a Vagrant definition file laying around for the stable-2.12 ppa
that let me bring up a vm easily. All seems fine.

How lttng is installed:

  add-apt-repository ppa:lttng/stable-2.12 -y
  apt-get update
  apt-get install -y lttng-tools lttng-modules-dkms babeltrace2 liblttng-ust-dev

From there all the steps for building the userspace application works without
ANY modifications.

The app is able to connect itself to the global sessiond: https://paste.ubuntu.com/p/QnfqbtgpFF/

Note that no local sessiond is present hence why the app does not communicate
with one.

Note that the user I am using here (vagrant) is not part of the "tracing" group
hence the user cannot interact with the global sessiond.

Such scenario return the following:

  vagrant@ubuntu2004:~$ lttng list -u
  Error: Unable to list UST events: No session daemon is available

Now let's start a lttng-sessiond for the user and restart our app (note that
this is not required for day to day tracing since a running app will connect
itself and only for debugging purpose):

 lttng-sessiond -b
 LTTNG_UST_DEBUG=1 ./hello

Yielding: https://paste.ubuntu.com/p/MsnHt94FXZ/

Now the app is connected to both sessiond.

Now the user can list the event against the local lttng-sessiond:

  vagrant@ubuntu2004:~$ lttng list -u
  UST events:
  -------------
  
  PID: 15429 - Name: ./hello
        lttng_ust_tracelog:TRACE_DEBUG (loglevel: TRACE_DEBUG (14)) (type: tracepoint)
        lttng_ust_tracelog:TRACE_DEBUG_LINE (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)


So based on this I would say that either we are not given the full picture of
what is going on or there is a step you are missing. One explication would be
that you end up linking against a older lttng-ust without knowing it.

Please run this an provide the output via a paste service:

   find /usr -name "*liblttng-ust*"

For example on my VM: https://paste.ubuntu.com/p/Tjxn3V7g5j/

Cheers

-- 
Jonathan Rajotte-Julien
EfficiOS
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Re: [lttng-dev] Issues on basic LTTng trace userspace (tutorial)

[MONTET Julien via lttng-dev]

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Hi Jonathan,

You are absolutely right !
I have two different lttng :   find /usr -name "*liblttng-ust*" Ubuntu Pastebin<https://paste.ubuntu.com/p/NVtXPhj4fW/>

According to you, what would be the best solution to solve this issue ?

I have indeed a folder named lttng-ust where I have made the (wrong) configure / make.

I tried to (temporary) remove all the libttng* /usr/local/lib/, but I face this problem :
/usr/bin/ld: hello-tp.o: in function `__lttng_events_init__hello_world':
hello-tp.c:(.text+0xe56): undefined reference to `lttng_ust_probe_register'
/usr/bin/ld: hello-tp.o: in function `__lttng_events_exit__hello_world':
hello-tp.c:(.text+0xeb2): undefined reference to `lttng_ust_probe_unregister'
collect2: error: ld returned 1 exit status

In the worst case scenario I am able to get my last clean snapchot.

What would you advise me to do ?

Cheers,

________________________________
De : Jonathan Rajotte-Julien <jonathan.rajotte-julien@efficios.com>
Envoyé : mercredi 24 mars 2021 17:36
À : MONTET Julien <julien.montet@reseau.eseo.fr>
Cc : lttng-dev <lttng-dev@lists.lttng.org>
Objet : Re: [lttng-dev] Issues on basic LTTng trace userspace (tutorial)

Hi Julien,

> 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.

Finally I had a Vagrant definition file laying around for the stable-2.12 ppa
that let me bring up a vm easily. All seems fine.

How lttng is installed:

  add-apt-repository ppa:lttng/stable-2.12 -y
  apt-get update
  apt-get install -y lttng-tools lttng-modules-dkms babeltrace2 liblttng-ust-dev

From there all the steps for building the userspace application works without
ANY modifications.

The app is able to connect itself to the global sessiond: https://paste.ubuntu.com/p/QnfqbtgpFF/

Note that no local sessiond is present hence why the app does not communicate
with one.

Note that the user I am using here (vagrant) is not part of the "tracing" group
hence the user cannot interact with the global sessiond.

Such scenario return the following:

  vagrant@ubuntu2004:~$ lttng list -u
  Error: Unable to list UST events: No session daemon is available

Now let's start a lttng-sessiond for the user and restart our app (note that
this is not required for day to day tracing since a running app will connect
itself and only for debugging purpose):

 lttng-sessiond -b
 LTTNG_UST_DEBUG=1 ./hello

Yielding: https://paste.ubuntu.com/p/MsnHt94FXZ/

Now the app is connected to both sessiond.

Now the user can list the event against the local lttng-sessiond:

  vagrant@ubuntu2004:~$ lttng list -u
  UST events:
  -------------

  PID: 15429 - Name: ./hello
        lttng_ust_tracelog:TRACE_DEBUG (loglevel: TRACE_DEBUG (14)) (type: tracepoint)
        lttng_ust_tracelog:TRACE_DEBUG_LINE (loglevel: TRACE_DEBUG_LINE (13)) (type: tracepoint)


So based on this I would say that either we are not given the full picture of
what is going on or there is a step you are missing. One explication would be
that you end up linking against a older lttng-ust without knowing it.

Please run this an provide the output via a paste service:

   find /usr -name "*liblttng-ust*"

For example on my VM: https://paste.ubuntu.com/p/Tjxn3V7g5j/

Cheers

--
Jonathan Rajotte-Julien
EfficiOS

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

[Jonathan Rajotte-Julien via lttng-dev]

On Wed, Mar 24, 2021 at 06:55:37PM +0000, MONTET Julien wrote:
> Hi Jonathan,
> 
> You are absolutely right !
> I have two different lttng :   find /usr -name "*liblttng-ust*" Ubuntu Pastebin<https://paste.ubuntu.com/p/NVtXPhj4fW/>

Glad to know that we are making progress.

> 
> According to you, what would be the best solution to solve this issue ?
> I have indeed a folder named lttng-ust where I have made the (wrong) configure / make.

Go into the lttng folder and do:
  sudo make uninstall
  sudo ldconfig

> 
> 
> I tried to (temporary) remove all the libttng* /usr/local/lib/, but I face this problem :

That should works also.

> /usr/bin/ld: hello-tp.o: in function `__lttng_events_init__hello_world':
> hello-tp.c:(.text+0xe56): undefined reference to `lttng_ust_probe_register'
> /usr/bin/ld: hello-tp.o: in function `__lttng_events_exit__hello_world':
> hello-tp.c:(.text+0xeb2): undefined reference to `lttng_ust_probe_unregister'
> collect2: error: ld returned 1 exit status

Did you remove the -L/usr/local/bin flag? There should be no reason to keep it
at this point.

> 
> In the worst case scenario I am able to get my last clean snapchot.

That is also a good bet :).

-- 
Jonathan Rajotte-Julien
EfficiOS
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Re: [lttng-dev] Issues on basic LTTng trace userspace (tutorial)

[MONTET Julien via lttng-dev]

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Hi Jonathan,

Thank you so much, it is 100% working.

Let's enjoy LTTng !!!

Have a nice day,

________________________________
De : Jonathan Rajotte-Julien <jonathan.rajotte-julien@efficios.com>
Envoyé : mercredi 24 mars 2021 20:00
À : MONTET Julien <julien.montet@reseau.eseo.fr>
Cc : lttng-dev <lttng-dev@lists.lttng.org>
Objet : Re: [lttng-dev] Issues on basic LTTng trace userspace (tutorial)

On Wed, Mar 24, 2021 at 06:55:37PM +0000, MONTET Julien wrote:
> Hi Jonathan,
>
> You are absolutely right !
> I have two different lttng :   find /usr -name "*liblttng-ust*" Ubuntu Pastebin<https://paste.ubuntu.com/p/NVtXPhj4fW/>

Glad to know that we are making progress.

>
> According to you, what would be the best solution to solve this issue ?
> I have indeed a folder named lttng-ust where I have made the (wrong) configure / make.

Go into the lttng folder and do:
  sudo make uninstall
  sudo ldconfig

>
>
> I tried to (temporary) remove all the libttng* /usr/local/lib/, but I face this problem :

That should works also.

> /usr/bin/ld: hello-tp.o: in function `__lttng_events_init__hello_world':
> hello-tp.c:(.text+0xe56): undefined reference to `lttng_ust_probe_register'
> /usr/bin/ld: hello-tp.o: in function `__lttng_events_exit__hello_world':
> hello-tp.c:(.text+0xeb2): undefined reference to `lttng_ust_probe_unregister'
> collect2: error: ld returned 1 exit status

Did you remove the -L/usr/local/bin flag? There should be no reason to keep it
at this point.

>
> In the worst case scenario I am able to get my last clean snapchot.

That is also a good bet :).

--
Jonathan Rajotte-Julien
EfficiOS

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