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<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">I tried different possibility to generate the userspace trace and kernel trace and observed that I’m not able to generate the user space tracing If the lttng-sessiond
is started<span style="color:#1F497D"><o:p></o:p></span></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">></span><span lang="EN-US"> using root user.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">></span><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">I’m using busybox in my custom Linux platform and no sudo support. It’s a 64 bit machine.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><b><span lang="EN-US">Trail 2:</span></b><span lang="EN-US" style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoPlainText"><b><span lang="EN-US" style="color:#1F497D">> </span></b><b><span lang="EN-US">========<o:p></o:p></span></b></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">></span><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">1. Start the lttng-session from root user<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">2. Run the following command from "tracing" group user<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">></span><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">lttng@/ # lttng -g lttng create
<b>ks</b><o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">Session ks created.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">Traces will be written in /home/lttng/lttng-traces/ks-20131224-123537<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">lttng@/ # lttng -g lttng enable-event -k -a<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">All kernel events are enabled in channel channel0<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">lttng@/ # lttng -g lttng start<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">Tracing started for session ks<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">lttng@/ # lttng -g lttng stop<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">Waiting for data availability.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><span lang="EN-US">Tracing stopped for session ks<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> […]</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> </span><b><span lang="EN-US">The kernel traces are generated fine<o:p></o:p></span></b></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> I can’t follow you on this one since my Ubuntu system doesn’t allow su (not easily, anyway). However, I’ll just point out that the lttng group option should not be used since it does not seem
to work at all (a problem I reported on the lttng-dev mailing list back on 9 July 2013, and which has remained unanswered so far).<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> According to the code, the lttng client checks if it belongs to the ‘group_name’ (default ‘tracing’) to decide which socket to ask for; in practice, whether a root lttng-sessiond is running
or not, if I’m not a member of ‘tracing’ it spawns a local lttng-sessiond whatever the specified group_name; conversely, if the root lttng-sessiond is running alone, I get to interrogate it regardless of the specified group_name if I’m a member of its ‘tracing’
group. What matters here is which group option value was used to launch lttng-sessiond. *That* works, forcing the root lttng-sessiond to accept unprivileged lttng client commands as privileged if the client is running in that group.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> Note that if you run a kernel and user-space trace as su, you will get two lttng-consumerd daemons, both running as root: one daemon handles the kernel events, the other the user-space events.
It’s easier to tell what is going on with the system monitor if you do not issue your commands from su. Stay in a normal user shell, and use sudo as required. (But you have no sudo support, you say…This’ll be tricky because I don’t have any su support!)<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> In the trails you explored, it would have been useful to know which groups your shell is a member of, and how the lttng-sessiond daemon was launched (i.e., which group it treats as the ‘tracing’
group).<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Trail 2:<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> [...]<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/ # lttng -g lttng create as<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Session as created.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Traces will be written in /home/lttng/lttng-traces/as-20131224-123811<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/ # lttng -g lttng enable-event -k -u -a<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> All kernel events are enabled in channel channel0<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/ # lttng -g lttng start<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Tracing started for session as<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/ # cd /tmp/<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/tmp # ./sample<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/tmp # lttng -g lttng stop<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Waiting for data availability.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Tracing stopped for session as<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/tmp # lttng -g lttng destroy<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> Session as destroyed<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> remove config file: Permission denied<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> lttng@/tmp # cd /home/lttng/lttng-traces/<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">> No userspace traces are generated<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> The “remove config file: Permission denied” you get is intriguing but a separate problem. What you did wrong here is to write:<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">lttng@/ # lttng -g lttng enable-event -k -u -a<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> thinking that this would enable both kernel and user-space events. It does not. The lttng client handles only one domain at a time. In this case, the -k option shadowed the -u option, which
was ignored. If you try it again with this:<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">lttng@/ # lttng -g lttng enable-event -k -a<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D">lttng@/ # lttng -g lttng enable-event -u -a<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> This time you should get both kernel and user-space events in the trace.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> As for trail 3, it does not capture any kernel events because it did not ask to capture any. You only enabled user-space events.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"> Hope this helps.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-US">Daniel U. Thibault<o:p></o:p></span></p>
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