Ssh – How to get/dump ssh client effective configuration without connecting

configurationssh

Question

Is there an equivalent for ssh to sshd -T (or, for those who know, something like maven's mvn help:effective-pom) ?

I'd like to be able to see the effective configuration that will be applied to an ssh command without having to / being able to connect to the remote host

Context

I've got batches with command line arguments, user local ~/.ssh/config and global /etc/ssh/ssh_config that bring nightmare config extrapolation problems.

Eg. command is failing because global config is forcing the remote port to the wrong ssh daemon / changed the remote username / changed the remote hostname /

Best Answer

In versions prior openssh-6.8 there is no way except -Q option, which is available only for [-Q cipher | cipher-auth | mac | kex | key]. You can get only some basic information about parsing ssh config during login with -v switch.

In openssh-6.8 and newer, there is switch for ssh, -G, which does the same as -T for sshd.

Related Solutions

SSH – How to Perform Diff Over SSH

You can do it with Bash's process substitution:

 diff foo <(ssh myServer 'cat foo')

Or, if both are on remote servers:

diff <(ssh myServer1 'cat foo') <(ssh myServer2 'cat foo')

Ssh – How to automate SSH login with password

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.