scp user1@host1:somefile user2@host2:somefile

Question

When I attempt to perform a

scp user1@host1:somfile user2@host2:somfile

I get

Host key verification failed.

lost connection

The authentication to both hosts is ssh-key based, however for security reasons the private key is only stored on the host that issues the above command.

Another complication in this setup is, that host2 is SFTP-only, so no shell access there.

I tested with an older openssl/openssh (Debian lenny openssh-client 5.1) combination and a with latest openssl/openssh releases built from source (openssl 1.0.0c, openssh 5.8) as well. Same behavior.

It's also woth to mention that executing

scp user1@host1:somfile somfile

scp somfile user2@host2:somfile

sequentially through a temp file works.

What am I'm doing wrong here?

Answer 1

Until OpenSSH 5.7, copying between two hosts is done directly. In other words, the connection to host2 is made from host1, using host1's list of known hostkeys.

• You can add host2 to the known_hosts file at host1, by simply connecting to it. Then use agent forwarding to let host1 authenticate using your locally running agent:

  ssh -oForwardAgent=yes host1 ssh host2 true
  
  scp -oForwardAgent=yes user1@host1:somfile user2@host2:
  

  (ssh has a shortcut -A for this option. It can also be added to ~/.ssh/config.)

• In 5.7 and later, you can use scp -3 to force the copy to be made through your computer:

  scp -3 user1@host1:somfile user2@host2:
  

  This will probably be much slower because of host1 → you → host2.

Answer 2

Don't you have ssh-agent running, do you?