Chapter 47: Debugging SSH with Verbose Mode
In this chapter, you'll learn how to use SSH verbose mode to debug connection issues, read handshake output, diagnose authentication failures, and interpret client and server side logs.
In the previous chapter, you learned how to use YubiKey and FIDO2 hardware security keys with SSH, generate ed25519-sk keys, and configure hardware-backed authentication that requires physical presence.
Now you're starting Module 14, where you'll learn how to debug, audit, log, and troubleshoot SSH connections.
Even with a secure SSH setup, you may still run into problems such as host key mismatches, authentication failures, connection timeouts, or port forwarding that doesn't work as expected.
When any of these issues occur, the quickest way to find the cause is to run SSH in verbose mode and carefully read its output.
In this chapter, you'll learn how to read and understand SSH's verbose output. You'll see what each verbosity level shows, how to identify common problems, and how to use the debug messages to quickly find the root cause.