scp between two remote servers in Python

Question

I am trying to connect a remote server using Paramiko and send some files to other remote server. I tried the code below, but it didn't work. I checked all connections, username and password parameters, they don't have any problem. Also the file which I want to transfer exist in first remote server in proper path.

The reason why I don't download files to my local computer and upload to second server is, connection speed between two remote servers is a lot faster.

Things that I tried:

• I set paramiko log level to debug, but couldn't find any useful information.

• I tried same scp command from first server to second server from command line, worked fine.

• I tried to log by data = stdout.readlines() after stdin.flush() line but that didn't log anything.

import paramiko
s = paramiko.SSHClient()
s.set_missing_host_key_policy(paramiko.AutoAddPolicy())
s.connect("10.10.10.10", 22, username='oracle', password='oracle', timeout=4)

stdin, stdout, stderr = s.exec_command(
        "scp /home/oracle/myFile.txt oracle@10.10.10.20:/home/oracle/myFile.txt")

stdin.write('password\n')
stdin.flush()
s.close()

Answer 1

You cannot write a password to the standard input of OpenSSH scp.

Try it in a shell, it won't work either:

echo password | scp /home/oracle/myFile.txt oracle@10.10.10.20:/home/oracle/myFile.txt

OpenSSH tools (including scp) read the password from a terminal only.

You can emulate the terminal by setting get_pty parameter of SSHClient.exec_command:

stdin, stdout, stderr = s.exec_command("scp ...", get_pty=True)
stdin.write('password\n')
stdin.flush()

Though enabling terminal emulation can bring you unwanted side effects.

A way better solution is to use a public key authentication. There also other workarounds. See How to pass password to scp? (though they internally have to do something similar to get_pty=True anyway).

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Other issues:

• You have to wait for the command to complete. Calling s.close() will likely terminate the transfer. Using stdout.readlines() will do in most cases. But it may hang, see Paramiko ssh die/hang with big output.
• Do not use AutoAddPolicy – You are losing a protection against MITM attacks by doing so. For a correct solution, see Paramiko "Unknown Server".