Passwordless ssh still asks for password when running as subprocess

Question

I had setup passwordless ssh (keygen) to access my remote workspace from my personal laptop. On the remote server, I do use an account with a password to connect. Setting up public/private key authentication allowed me to connect without having to type this password.

The Python script I am running uses subprocess.Popen() to ssh into this remote workspace again. However, it is not a passwordless ssh during this. I have checked my permissions and have tried to delete and recreate the keys, yet this still happens.

Below is the relevant piece of Python code.

subprocess.Popen(['ssh', machine_addr, 'cd ' + workspace + \ '; python dispynode.py --serve 1 --clean --dest_path_prefix dispytmp_' + str(i)])

Answer 1

I know this question has been asked 4 years ago but I faced the same problem and found an explanation and a solution which worked for me, so this might be helpful for other people in the same situation.

Context

Same as you, I generated and shared the ssh keys between my client (Raspberry Pi) and my server. I was able to connect via ssh with no password prompt running ssh user@server. But when my Python script tried to connect with subprocess.Popen, it asked for a password.

Explanation

The thing is I run my Python script with sudo because for some reasons I need to.

So the ssh command ran by subprocess.Popen used as ssh key the one located at /root/.ssh/id_rsa, while the one generated and shared with the server was located at /home/user/.ssh/id_rsa.

Solution

Add as argument to the ssh command the correct identification file :

ssh -i /home/user/.ssh/id_rsa user@server

So the Python line you need is the following :

subprocess.Popen(['ssh', '-i', '/home/user/.ssh/id_rsa', 'user@server']

To which you add the commands you want (cd, mkdir, etc).

Hope this helps !