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My setup is the following:

  • node A is where I start
  • node B is the gateway machine
  • node C is the destination.

From Ato B I have setup SSH public key authentication but from B to C I am not allowed to.

So from node A I use the following incantation which actually works from a different machine (Ubuntu 14.04):

sshpass -p secretpass ssh -oProxyCommand="ssh -W %h:%p username@B" username@C

… however, when I try from a different location with another machine (Ubuntu 16.04 - though I doubt that's relevant), the invocation of sshpass promptly returns without any kind of output and an exit code (obtained with echo $?) of 6.

More puzzling is the fact that if I do the steps separately, they succeed:

A: $ ssh username@B   (directly access B without being prompted for password)
B: $ ssh username@C   (prompted for password, provided 'secretpass')
C: $                  (reached my destination)
  • I don't have a similar setup to test, but will ssh -A -t username@B sshpass -p secretpass ssh -A username@C work? – Paul H. Nov 16 '16 at 16:28
  • sshpass is not available on node B nor can I install it. – Marcus Junius Brutus Nov 16 '16 at 16:50
4

Ok, so I figured out what was the matter. Since I was using this script for the first time on this machine I had to first do the following (without sshpass):

ssh -oProxyCommand="ssh -W %h:%p username@B" username@C

I was then prompted with:

The authenticity of host 'C <no hostip for proxy command>)' can't be established.

RSA key fingerprint is SHA256:... .

Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added 'C' (RSA) to the list of known hosts

… once I accepted the above, I was able to use the incantation I inquire about in my question without further problems.

So this failure was due to the incantation not being able to answer to the authenticity prompt that only appears once.

  • Please remember to log in once with all used users. At first I only did it with a normal user and then wondered why the script (executed with sudo/root!) didn't work. -_- – uav Jun 25 at 13:26

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