It started with a silent freeze on the terminal. One moment, packets were flowing. The next, Mosh had stopped talking. No error. No warning. Just stillness.
Debugging Mosh isn’t about guessing. It’s about seeing exactly what it’s doing under the hood. That means unlocking Mosh debug logging access and reading the raw truth.
Mosh, the mobile shell, is famous for keeping connections alive over spotty networks. But when things go wrong, the same persistence that makes it useful can hide the real cause. Debug logging turns its core behavior into a readable trace—timestamps, state transitions, packet events. This is where silent bugs reveal themselves.
The process starts simple. Launch Mosh with the --verbose flag or set MOSH_DEBUG in the environment. You can push the logging higher with repeated --verbose entries or compile with debug symbols to get the deepest signal data. Output sends to STDERR by default, so redirecting it to a file captures the full session for later analysis. These debug logs let you track handshake details, predictive echo timing, UDP port negotiations, and even loss recovery behavior frame by frame.