Failed to create an SFTP client: Authentication failed

Just testing vertical backup on my ESXI server (6.7 - free license).

Backing up over SFTP with password works fine however attempts to use ssh keys fail with the following error:

[root@esxi:/vmfs/volumes/5950cec4-139b2712-ec87-0cc47a9a5c3a/verticalbackup] ./vertical list
Vertical Backup 1.4.3’s password (leave blank to choose public key authentication):
Enter the path of the ssh private key file:nas.ssh
Enter the passphrase of the ssh private key file:
Failed to create an SFTP client: Authentication failed.

However it works find from the same box using ssh:

[root@esxi:/vmfs/volumes/5950cec4-139b2712-ec87-0cc47a9a5c3a/verticalbackup] ssh -i nas.ssh duplicacy@nas id
Enter passphrase for key ‘nas.ssh’:
uid=1001(duplicacy) gid=1001(duplicacy) groups=1001(duplicacy)

Tried using keys with and without passphrases. Verbose output gives no extra information.

Logs on nas box (Raspbian GNU/Linux 10 (buster)) :

Jul 22 12:48:05 nas sshd[11426]: Connection closed by authenticating user duplicacy port 16183 [preauth]

Any ideas?


How did you generate the ssh private key? The first line must be -----BEGIN RSA PRIVATE KEY----- or -----BEGIN DSA PRIVATE KEY-----.