contents/getting-started/tracing-the-linux-kernel.md

   1 ---
   2 id: tracing-the-linux-kernel
   3 ---
   4
   5 Make sure LTTng-tools and LTTng-modules packages
   6 [are installed](#doc-installing-lttng).
   7
   8 Since you're about to trace the Linux kernel itself, let's look at the
   9 available kernel events using the `lttng` tool, which has a
  10 Git like command line structure:
  11
  12 <pre class="term">
  13 lttng list --kernel
  14 </pre>
  15
  16 <div class="tip">
  17 <p>
  18     <span class="t">Tip:</span>You can avoid using <code>sudo</code> in
  19     the previous and following commands if your user is part of the
  20     <a href="/docs/#doc-lttng-sessiond"><code>tracing</code> group</a>.
  21 </p>
  22 </div>
  23
  24 Before tracing, you need to create a session:
  25
  26 <pre class="term">
  27 sudo lttng create my-session
  28 </pre>
  29
  30 `my-session` is the tracing session name and could be anything you
  31 like. `auto` will be used if omitted.
  32
  33 Let's now enable some events for this session:
  34
  35 <pre class="term">
  36 sudo lttng enable-event --kernel sched_switch,sched_process_fork
  37 </pre>
  38
  39 or you might want to simply enable all available kernel events (beware
  40 that trace files will grow rapidly when doing this):
  41
  42 <pre class="term">
  43 sudo lttng enable-event --kernel --all
  44 </pre>
  45
  46 Start tracing:
  47
  48 <pre class="term">
  49 sudo lttng start
  50 </pre>
  51
  52 By default, traces are saved in
  53 <code>~/lttng-traces/<em>name</em>-<em>date</em>-<em>time</em></code>,
  54 where <code><em>name</em></code> is the session name.
  55
  56 When you're done tracing:
  57
  58 <pre class="term">
  59 sudo lttng stop
  60 sudo lttng destroy
  61 </pre>
  62
  63 Although `destroy` looks scary here, it doesn't actually destroy the
  64 outputted traces: it only destroys the tracing session.
  65
  66 What's next? Have a look at
  67 [Viewing and analyzing your traces](#doc-viewing-and-analyzing-your-traces)
  68 to view and analyze the trace you just recorded.