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Merge pull request #8076 from qlyoung/doc-lttng-fork-preload

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doc: document LD_PRELOAD workaround for lttng
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Donatas Abraitis 2021-02-13 10:43:44 +02:00 committed by GitHub
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doc/developer/tracing.rst
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@ -308,6 +308,31 @@ Limitations
Tracers do not like ``fork()`` or ``dlopen()``. LTTng has some workarounds for Tracers do not like ``fork()`` or ``dlopen()``. LTTng has some workarounds for
this involving interceptor libraries using ``LD_PRELOAD``. this involving interceptor libraries using ``LD_PRELOAD``.
If you're running FRR in a typical daemonizing way (``-d`` to the daemons)
you'll need to run the daemons like so:
.. code-block:: shell
LD_PRELOAD=liblttng-ust-fork.so <daemon>
If you're using systemd this you can accomplish this for all daemons by
modifying ``frr.service`` like so:
.. code-block:: diff
--- a/frr.service
+++ b/frr.service
@@ -7,6 +7,7 @@ Before=network.target
OnFailure=heartbeat-failed@%n.service
[Service]
+Environment="LD_PRELOAD=liblttng-ust-fork.so"
Nice=-5
Type=forking
NotifyAccess=all
USDT tracepoints are relatively high overhead and probably shouldn't be used USDT tracepoints are relatively high overhead and probably shouldn't be used
for "flight recorder" functionality, i.e. enabling and passively recording all for "flight recorder" functionality, i.e. enabling and passively recording all
events for monitoring purposes. It's generally okay to use LTTng like this, events for monitoring purposes. It's generally okay to use LTTng like this,