Debugging LND
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
Logging is useful for security and operating purposes. LND logs can typically be found on Linux at ~/.lnd/logs/bitcoin/mainnet/lnd.log, on macOS at ~/Library/Application Support/Lnd/logs/bitcoin/mainnet or in their specified location using the--logdir flag at startup.
By default, LND will log 10MB worth of its history, and additionally keep three blocks of logs around, compressed with gzip as lnd.log.<i>.gz in the same directory.
You can adjust the location of your log files as well their maximum size (in MB) and how many historical log files you expect LND to keep, in your lnd.conf file.
logdir=~/.lnd/logs
maxlogfiles=3
maxlogfilesize=10
debuglevel=debug,PEER=info
Additionally, the debuglevel can be overridden and adjusted without requiring a restart using the command lncli debuglevel --level=
The available debug levels are, in order of descending detail: trace, debug, info, warn, error, critical, off
Example usage:
lncli debuglevel –-level=debug
Additionally, the log level can be adjusted for each individual subsystem. A list of the subsystem can also be obtained with the command lncli debuglevel --show
Varying debug levels for multiple subsystems can be chained together with commands.
Example usage:
debuglevel --level=BTCN=trace,LNWL=debug
Subsystems:
Capturing pprof data with lnd
lndlnd 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.
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:
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