contents/using-lttng/controlling-tracing/sending-trace-data-over-the-network.md

   1 ---
   2 id: sending-trace-data-over-the-network
   3 ---
   4
   5 The possibility of sending trace data over the network comes as a
   6 built-in feature of LTTng-tools. For this to be possible, an LTTng
   7 _relay daemon_ must be executed and listening on the machine where
   8 trace data is to be received, and the user must create a tracing
   9 session using appropriate options to forward trace data to the remote
  10 relay daemon.
  11
  12 The relay daemon listens on two different TCP ports: one for control
  13 information and the other for actual trace data.
  14
  15 Starting the relay daemon on the remote machine is easy:
  16
  17 <pre class="term">
  18 lttng-relayd
  19 </pre>
  20
  21 This makes it listen to its default ports: 5342 for control and
  22 5343 for trace data. The `--control-port` and `--data-port` options may
  23 be used to specify different ports.
  24
  25 Traces written by `lttng-relayd` are written to
  26 <code>~/lttng-traces/<em>hostname</em>/<em>session</em></code> by
  27 default, where <code><em>hostname</em></code> is the host name of the
  28 traced (monitored) system and <code><em>session</em></code> is the
  29 tracing session name. Use the `--output` option to write trace data
  30 outside `~/lttng-traces`.
  31
  32 On the sending side, a tracing session must be created using the
  33 `lttng` tool with the `--set-url` option to connect to the distant
  34 relay daemon:
  35
  36 <pre class="term">
  37 lttng create my-session --set-url net://distant-host
  38 </pre>
  39
  40 The URL format is described in the output of `lttng create --help`.
  41 The above example uses the default ports; the `--ctrl-url` and
  42 `--data-url` options may be used to set the control and data URLs
  43 individually.
  44
  45 Once this basic setup is completed and the connection is established,
  46 you may use the `lttng` tool on the target machine as usual; everything
  47 you do is transparently forwarded to the remote machine if needed.
  48 For example, a parameter changing the maximum size of trace files
  49 only has an effect on the distant relay daemon actually writing
  50 the trace.