Debugging LND

  1. Overview


lnd ships with a few useful features for debugging, such as a built-in profiler and tunable logging levels. If you need to submit a bug report for lnd, it may be helpful to capture debug logging and performance data ahead of time.

Debug Logging

You can enable debug logging in lnd by passing the --debuglevel flag. For example, to increase the log level from info to debug:

⛰ lnd --debuglevel=debug

You may also specify logging per-subsystem, like this:

⛰ lnd --debuglevel=<subsystem>=<level>,<subsystem2>=<level>,...

Capturing pprof data with lnd

lnd has a built-in feature which allows you to capture profiling data at runtime using pprof, a profiler for Go. The profiler has negligible performance overhead during normal operations (unless you have explicitly enabled CPU profiling).

To enable this ability, start lnd with the --profile option using a free port.

⛰ lnd --profile=9736

Now, with lnd running, you can use the pprof endpoint on port 9736 to collect runtime profiling data. You can fetch this data using curl like so:

⛰ curl http://localhost:9736/debug/pprof/goroutine?debug=1