Unable to start Plesk migration or connect via SSH Terminal extension due to invalid permissions on .ssh files: Permission denied (publickey,gssapi-with-mic,password)

Symptoms

• Plesk migration fails with the following error message in Plesk:

  Failed to fetch basic information about resellers, clients and domains data from source servers
  <...>
  stderr: Permission denied (publickey,gssapi-with-mic,password).
  rsync: connection unexpectedly closed (0 bytes received so far) [sender]
  rsync error: unexplained error (code 255) at io.c(605) [sender=3.0.9]

• Plesk admin user cannot access the server via SSH using the SSH Terminal extension:

  Connection Broken

• One of the following error messages appears in the logfile /var/log/secure (CentOS/RHEL) or /var/log/auth.log (Debian/Ubuntu) on the source server:

  Authentication refused: bad ownership or modes for directory /root

  ---

  Authentication refused: bad ownership or modes for directory /root/.ssh

  ---

  Authentication refused: bad ownership or modes for file /root/.ssh/authorized_keys

Cause

Wrong permissions on the directories /root or /root/.ssh or files inside /root/.ssh.

Resolution

1. Connect to the source server via SSH.

2. Run the commands below to correct permissions:

   • on the /root directory:

     # chmod 550 /root
     # chown root:root /root

   • on the /root/.ssh directory:

     # chown -R root:root /root/.ssh
     # chmod 600 /root/.ssh

   • on the files inside /root/.ssh:

     # chmod 600 /root/.ssh/*