Migration cannot be started: administrator login and/or password are not correct

Symptoms

• Unable to start migration with one of the following error messages:

  PLESK_ERROR: SSH connection to the source server can not be used: there is unexpected output when executing commands. Clean output is required by migrator to execute commands and consume their output, and to run "rsync" tool (for file transfer) which uses SSH connection as transport and does not work if there is any unexpected output.

  PLESK_ERROR: Failed to fetch basic information about resellers, clients and domains data from source servers
  Cause: Command execution failed on the local server with non-zero exit code.
  command: /bin/mkdir -p /root/plesk_migrator
  exit code: 1
  stdout:
  stderr: /bin/mkdir: cannot create directory '/root': Permissions denied
  
  That is a critical error, migration was stopped.

• Migration fails with one of the following error messages:

  PLESK_ERROR: Error message or request description : Error: launchpad error (Error code = 2): == STDERR ==================== Cannot request remote agent status using command line /var/cache/2013100110274185/PleskX.pl: Died at AgentConfig.pm line 23. at AgentConfig.pm line 23 AgentConfig::AUTOLOAD() called at /var/cache/2013100110274185/PleskX.pl line 298 main::writeMigrationResult() called at /var/cache/2013100110274185/PleskX.pl line 304

  PLESK_ERROR: Cannot request remote agent status using command line /var/cache/20150318093912860/PleskX.pl: which: no ruby in (/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin)
  Can't open perl script "/var/cache/20150318093912860/PleskX.pl": No such file or directory

Cause

A non-root user is specified for migration.

Resolution

Specify the "root" credentials for the source server in order to start a migration. Alternatively, choose to authenticate via SSH keys. For details, refer to Authentication by SSH (Linux).

Note: It is possible to migrate with a non-root user in case of Migrating From a Linux Server With Custom Hosting.

Additional Information

If the article did not help, check root user authentication configuration on the source server as per this article