Debug logging

When you report a bug, the developer will almost always ask for debug logs. This page tells you how to enable them, where to find them, and how to share them safely.

Why debug logs?

A normal log line says “something happened”. A debug log line says why it happened and what data was involved. For an audio glitch, the difference is between:

info: voice frame dropped

and

debug: voice frame dropped: jitter buffer late by 47ms (threshold 30ms), last 3 frames late

App: enable debug logging

1. Open Settings, Advanced.

2. Find the Log level dropdown (Expert mode required).

3. Pick:

   • info for normal operation (default).
   • debug for the issue you are reporting.
   • trace for the most detail. Massive log files, use sparingly.

4. Reproduce the problem while debug logging is on. Try to make the minimum reproduction so the log stays short.

5. Switch back to info afterwards. Debug logging is expensive on disk and CPU.

 Screenshot placeholder: advanced settings with the log level dropdown set to debug.

App: where is the log file?

The location depends on your operating system.

Windows

Windows

%APPDATA%\com.fancy-mumble.app\logs\fancy-mumble.log

In Explorer, paste %APPDATA%\com.fancy-mumble.app\logs into the address bar.

Linux

Linux

~/.local/share/com.fancy-mumble.app/logs/fancy-mumble.log

Or, with the AppImage build:

~/.fancy-mumble/logs/fancy-mumble.log

macOS

macOS

~/Library/Logs/com.fancy-mumble.app/fancy-mumble.log

Android

Android

The app cannot easily expose the log file. Use Settings, Advanced, Export logs to get a zip that you can save or share.

The folder also contains rotated archives:

• fancy-mumble.log is the live file.
• fancy-mumble.log.1, .2, … are previous sessions.

Server: enable verbose logging

Environment variable

environment:
  MUMBLE_VERBOSE: true

Restart the container. Logs now include info and debug lines.

Per-component

Mumble has separate log channels per plugin. Set in your custom INI:

plugin.webrtc-sfu.logLevel=debug
plugin.file-server.logLevel=debug
plugin.link-previews.logLevel=debug
plugin.push-fcm.logLevel=debug
plugin.persistent-chat.logLevel=debug

Useful when one feature misbehaves and you do not want the noise of all the others.

Server: where to read the log

# Live:
docker compose logs -f mumble-server

# Last 1000 lines:
docker compose logs --tail=1000 mumble-server > server.log

For long-running diagnostics, redirect to a file:

docker compose logs -f mumble-server > server.log 2>&1 &
# ... reproduce the issue ...
kill %1

Redacting before you share

Before posting a log on GitHub or in chat, strip personally identifying data:

• Your public IP (search and replace with 1.2.3.4).
• Tokens in the form Authorization: Bearer ....
• Push credentials (rare in logs, but check).
• Other users’ usernames if your community values privacy.

A quick one-liner:

sed -E -e 's/[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+/1.2.3.4/g' \
       -e 's/Authorization: [^[:space:]]*/Authorization: [REDACTED]/g' \
  fancy-mumble.log > fancy-mumble.redacted.log

What to include in a bug report

The good report formula

1. Steps to reproduce, minimum reproduction.
2. Expected vs observed behavior.
3. The app version and server version.
4. Operating system and version.
5. Network setup (home, office, mobile, VPN).
6. The debug log for the reproduction window, redacted.

A round trip example

You: “audio cuts mid-sentence”.

Developer: “can you enable debug logging and reproduce with a 10- second sample?”

You:

1. Settings, Advanced, Log level, debug.
2. Reconnect to the server.
3. Talk for 10 seconds with a friend in the call, including the moment the cut happens.
4. Disconnect.
5. Grab the log file, redact.
6. Attach to the issue.

Developer: “the audio packet seq=4231 was dropped because the jitter buffer was full. Increase jitterBufferSize in your config to 200.” Issue closed.

That round trip would take an extra five messages without debug logs.

Real-time tracing (advanced)

Both client and server can stream events to a TCP listener for live diagnosis. Set:

environment:
  MUMBLE_TRACE_TCP: "192.0.2.5:4444"

A nc -l 4444 on the listener side captures everything. Useful for sessions where you cannot reproduce locally.

Next step

You are ready to file a bug report. Head to Reporting bugs for the checklist.