Question Plesk Migration: How to connect via SSH to Source Server (help needed after many trials)

[TomyByte]

Server operating system version

Ubuntu 22.04.4 LTS

Plesk version and microupdate number

18.0.62 #2

Systems Target and Source are:
Ubuntu 22.04.4 LTS, Plesk Obsidian: Version 18.0.62 Update #2 - TCP Ports: 22, 8443, 110 and 143 opened on both. SSH-Connections allowed on both.

With my last migration some times ago I firstly had the same issues (no connection via password possible and ssh connection failed) but then I could connect, the credentials (data and keys) didn't work this time. I generated several different key pairs (without a passphrase) they all don't worked. In my last trial I used this data:
SSH-Keys created through:
(also: ssh-keygen -b512 -t ecdsa)
ssh-keygen -b256 -t ecdsa
root-Login: root
path to private key on target server: /root/.ssh/id_ecdsa
path to private key on source server: /root/.ssh/id_ecdsa.pub
info.log:
[ERROR] Unable to connect to [Source Server IP] by SSH: Invalid key
debug.log:
"/opt/plesk/python/3/lib/python3.10/site-packages/paramiko/ed25519key.py", line 114, in _parse_signing_key_data
=| raise SSHException("Invalid key")

I have no idea left, how to solve this connection problem.

Is here someone to help?

Thank you in advance

Tom

 

[TomyByte]

Additional remark: In the directory on source server I created both keys with the command above, then I copied via local copy (WinSCP) the private key to the target server. Can this be an issue?

 

[TomyByte]

Error correction for #1: it should read: path to public key on source server: ...

 

[La Linea]

Additional remark: In the directory on source server I created both keys with the command above, then I copied via local copy (WinSCP) the private key to the target server. Can this be an issue?

When you want to connect as root from the target server to the source server, you create the keypair as root on the target server.

Then you "copy" the (public) key via ...

ssh-copy-id -i ~/.ssh/mykey root@source-server

This doesn't copy the key.pub as a file, but adds it to ~/.ssh/authorized_keys file.

The private key MUST never be copied to any other system!

Please see What is ssh-copy-id? How ssh-copy-id works? for further information and additional troubleshooting.