"Error: Authentication failed on fileserver sftp" when configuring VMware NSX on Linux server

Products

• VMware NSX

Issue/Introduction

• This is a new NSX backup configuration to a Linux backup server.
• The destination server uses the supported operating system and Openssh versions, as per the Administration guide Configure Backups.
• SFTP works to the destination server from NSX as the user.
• Using the steps in this KB "Authentication failed", "bad directory" or "server disk full" error when preforming NSX backup to Windows SFTP server in the Resolution section, to test the destination server, by adding a test file also works.
• Using ket scan to check valid keys on the backup server shows ecdsa is available:

ssh-keyscan -t ecdsa localhost  

• NSX manager syslog shows the following log entry:

nsx@6876 comp="nsx-manager" errorCode="MP29115" level="ERROR" s2comp="backup-restore" subcomp="manager"] Inventory backup failed with ; BackupAsyncStatus [BackupStatus [status=AUTH_FAILURE, statusDetail=Cannot connect to sftp server. The remote server returned error: status: 255   out: '[Errno 5] Input/output error'., remoteUri=sftp://<destination-backup-server>:22/<path>/inventory-summary, errorCode=null, startTime=##############, endTime=##############]; responseBody=null].

Environment

VMware NSX

Resolution

This issue occurs when there is a permissions issue with the user, the directory or another environmental issue.

To rule NSX in or out, deploy a fresh Ubuntu 20.04 server, no modifications.

Install openssh 'sudo apt install openssh-server'

Create a directory 'mkdir /home/<user>/backup/NSX'

Then configure NSX to use this new server, use the IP address, instead of the FQDN also to avoid possible DNS issue.

This should now work.

If not and there may be security devices in between the NSX manager and the backup server, move the backup server to the same portgroup and subnet as the NSX manager and test again.