7.3. 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:

# SSH1, SSH2, OpenSSH
$ 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 [Section 12.3, "Other SSH Resources"], 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
[email protected]'s password:

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

$ ssh -v server.example.com
SSH Version 1.2.27 [sparc-sun-solaris2.5.1], protocol version 1.5.
client: Connecting to server.example.com [128.9.176.249] port 22.
client: Connection established.
client: Trying RSA authentication with key 'barrett@client'
client: Remote: Bad file modes for /users/barrett/.ssh                Uh oh!

client: Server refused our key.
client: Doing password authentication.
[email protected]'s password:

These messages (which are abbreviated for this example) confirm that the SSH connection is succeeding, but public-key authentication is failing. The reason is "bad file modes": the remote SSH directory, /home/barrett/.ssh, has incorrect permissions. A quick trip to the server and a well-placed chmod command later, the problem is solved:

# On the server
$ chmod 700 ~/.ssh

Verbose mode also works for scp :

$ scp -v myfile server.example.com:
Executing: host belvedere, user (unspecified), command scp -v -t .
SSH Version 1.2.27 [sparc-sun-solaris2.5.1], protocol version 1.5.
...

Verbose mode is your friend. Use it liberally. Now we're ready to learn those dozens of options.

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