Unable to start a Plesk migration: bin/mkdir: cannot create directory: Permission denied

Symptoms

When starting a Plesk migration, the preparation fails with one of the following error messages:

PLESK_ERROR: Failed to perform action: Fetch data from source cPanel
Cause: Command execution failed on the source server 'cpanel' (203.0.113.2) with non-zero exit code.
command: /bin/mkdir -p /home/user/public_html/plesk_migrator
exit code: 1
stdout:
stderr: /bin/mkdir: cannot create directory `/home/user': Permission denied
That is a critical error, migration was stopped.

PLESK_ERROR: Failed to fetch basic information about resellers, clients and domains data from source servers Cause: Command execution failed on the source server 'source' (203.0.113.2) with non-zero exit code. command: /bin/mkdir -p /root/plesk_migrator exit code: 1 stdout: stderr: /bin/mkdir: cannot create directory ‘/root’: Permission denied
That is a critical error, migration was stopped.

PLESK_ERROR: Failed to perform action: Fetch shallow data from source cPanel
Cause: Error while connecting to the the source server 'cpanel' (203.0.113.2) at '203.0.113.2' by SSH as 'exampleuser': Unable to connect to '203.0.113.2' by SSH: [Errno 110] Connection timed out.
Ensure that the server is up and there are no firewall rules that may block SSH connections to the server, then restart migration. That is a critical error, migration was stopped.

PLESK_ERROR: Could not connect to the target server. ssh: handshake failed: ssh: unable to authenticate, attempted methods [none password], no supported methods remain

PLESK_ERROR: Failed to fetch basic information about resellers, clients and domains data from source servers
...
stderr: /bin/mkdir: cannot create directory ‘/root’: Permission denied

PLESK_ERROR: Failed to fetch basic information about resellers, clients and domains data from source servers
...
stderr: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
rsync: connection unexpectedly closed (0 bytes received so far) [sender]

PLESK_ERROR: SSH connection to the source server 'source' (203.0.113.2) can not be used: command "bin/true" executed by SSH returned non-zero exit code. Check that the user used to connect to the server has "/bin/sh" or "/bin/bash" as its shell.

Cause

Migration was started using a user with sudo rights.

For Plesk migration, only a built-in 'root' user will work.

Resolution

Start a new Plesk migration session using the 'root' user and its password.

If the 'root' user is disabled on the source server, enable it using the steps from this KB article.

Note: To learn more about Plesk Migrator limitations, see this KB article.