'Backup Manager encountered an exception' error during vCenter VAMI Backup using SFTP

Products

• VMware vCenter Server

Issue/Introduction

• SFTP backup fails during data transfer with error "Backup Manager encountered an exception. See logs for details".
• The following errors are logged in the /var/log/vmware/applmgmt/backup.log file:
  
  ERROR: rc: 120, stderr: Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='utf-8'>
BrokenPipeError: [Errno 32] Broken pipe

Err: curl: (2) Failure establishing ssh session: -43, Failed getting banner

Environment

VMware vCenter Server 7.x
VMware vCenter Server 8.x

Cause

The issue occurs due to a limitation of concurrent SSH Sessions on the SFTP Server.

This can affect the functionality of the SFTP Backup because the file transfers are initiated in parallel in VCSA.

Resolution

Below are the steps to change the File Transfer Mode to 'Serial' that will prevent the creation of concurrent SSH sessions:

1. 1. SSH to the vCenter Server as root.
      
      
   2. Take a backup of file appliance.conf:
      
      cp /etc/applmgmt/appliance/appliance.conf /storage/appliance.conf.bak


   3. Edit the file:
      
      vi /etc/applmgmt/appliance/appliance.conf


   4. Change the below line:
      
      "fileTransferMode": "parallel",
      
      to 
      
"fileTransferMode": "serial",
      
      
   5. Save the file:
      
      Hit Esc -> :wq!  


   6. Restart applmgmt service:
      
      service-control --restart applmgmt