SSH, The Secure Shell: The Definitive Guide, 2nd Edition

Introduction to Verbose Mode

Now that we’ve covered the generalities of command-line options and configuration files, we’re about to launch into an extended discussion of configuration. Before we begin, let’s practice some defense. As you try these options, occasionally you might see behavior that’s not what you expected. Whenever this occurs, your first instinct should be: turn on verbose mode with the -v command-line option to track down the problem:

    $ ssh -v server.example.com

In verbose mode, the client prints messages as it proceeds, providing clues to the problem. New SSH users (and quite a few experienced ones) frequently forget or neglect to use verbose mode when problems arise. Don’t hesitate! Many questions we’ve seen in the Usenet SSH newsgroup, comp.security.ssh [12.3], could have been answered immediately by running ssh -v and examining the output.

Suppose you just installed your public key on server.example.com and are trying to authenticate with it. Strangely, you are prompted for your login password instead of your public-key passphrase:

    $ ssh server.example.com
    [e-mail]'s password:

Don’t just sit there scratching your head in wonder. Let verbose mode come to the rescue:

 $ ssh -v server.example.com OpenSSH_3.8p1, SSH protocols 1.5/2.0, OpenSSL 0.9.7d 17 Mar 2004 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to server.example.com [192.168.0.10] port 22. debug1: Connection established. debug1: ...