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5e0cbfb0 PP |
1 | --- |
2 | id: lttng-relayd | |
3 | --- | |
4 | ||
5 | When a tracing session is configured to send its trace data over the | |
6 | network, an LTTng _relay daemon_ must be used at the other end to | |
7 | receive trace packets and serialize them to trace files. This setup | |
8 | makes it possible to trace a target system without ever committing trace | |
9 | data to its local storage, a feature which is useful for embedded | |
10 | systems, amongst others. The command implementing the relay daemon | |
11 | is `lttng-relayd`. | |
12 | ||
13 | The basic use case of `lttng-relayd` is to transfer trace data received | |
14 | over the network to trace files on the local file system. The relay | |
15 | daemon must listen on two TCP ports to achieve this: one control port, | |
16 | used by the target session daemon, and one data port, used by the | |
17 | target consumer daemon. The relay and session daemons agree on common | |
18 | default ports when custom ones are not specified. | |
19 | ||
20 | Since the communication transport protocol for both ports is standard | |
21 | TCP, the relay daemon may be started either remotely or locally (on the | |
22 | target system). | |
23 | ||
24 | While two instances of consumer daemons (32-bit and 64-bit) may run | |
25 | concurrently for a given user, `lttng-relayd` needs only be of its | |
26 | host operating system's bitness. | |
27 | ||
28 | The other important feature of LTTng's relay daemon is the support of | |
29 | _LTTng live_. LTTng live is an application protocol to view events as | |
47bfcb75 | 30 | they arrive. The relay daemon still records events in trace files, |
ecccc788 PP |
31 | but a _tee_ allows to inspect incoming events. |
32 | ||
5703c9f3 | 33 | <figure class="img img-100"> |
ecccc788 | 34 | <img src="/images/docs26/lttng-live.png" alt="LTTng live"> |
d9a0e8b1 PP |
35 | <figcaption> |
36 | The relay daemon creates a <em>tee</em>, forwarding the trace data | |
37 | to both trace files and a live viewer. | |
38 | </figcaption> | |
5703c9f3 | 39 | </figure> |
ecccc788 PP |
40 | |
41 | Using LTTng live | |
5e0cbfb0 | 42 | locally thus requires to run a local relay daemon. |