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[lttng-docs.git] / contents / getting-started / tracing-the-linux-kernel.md

---
id: tracing-the-linux-kernel
---

Make sure LTTng-tools and LTTng-modules packages
[are installed](#doc-installing-lttng).

Since you're about to trace the Linux kernel itself, let's look at the
available kernel events using the `lttng` tool, which has a
Git like command line structure:

<pre class="term">
lttng list --kernel
</pre>

<div class="tip">
<p>
    <span class="t">Tip:</span>You can avoid using <code>sudo</code> in
    the previous and following commands if your user is part of the
    <a href="/docs/#doc-lttng-sessiond" class="int"><code>tracing</code> group</a>.
</p>
</div>

Before tracing, you need to create a session:

<pre class="term">
sudo lttng create my-session
</pre>

`my-session` is the tracing session name and could be anything you
like. `auto` will be used if omitted.

Let's now enable some events for this session:

<pre class="term">
sudo lttng enable-event --kernel sched_switch,sched_process_fork
</pre>

or you might want to simply enable all available kernel events (beware
that trace files will grow rapidly when doing this):

<pre class="term">
sudo lttng enable-event --kernel --all
</pre>

Start tracing:

<pre class="term">
sudo lttng start
</pre>

By default, traces are saved in
<code>~/lttng-traces/<em>name</em>-<em>date</em>-<em>time</em></code>,
where <code><em>name</em></code> is the session name.

When you're done tracing:

<pre class="term">
sudo lttng stop
sudo lttng destroy
</pre>

Although `destroy` looks scary here, it doesn't actually destroy the
outputted traces: it only destroys the tracing session.

What's next? Have a look at
[Viewing and analyzing your traces](#doc-viewing-and-analyzing-your-traces)
to view and analyze the trace you just recorded.