How to Troubleshoot vCenter Too Many Authentication Failures

Are you tired of dealing with frustrating authentication failures when accessing your vCenter environment? In this article, we delve into the intricacies of vCenter authentication, exploring the common types of SSH errors and shedding light on the dreaded "Too Many Authentication Failures" message.


By Zelia / Updated on August 25, 2023

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The basic authentication process involved when accessing vCenter

Authentication, in the context of vCenter, is the process of verifying the identity of a user or system attempting to access the management interface. It establishes trust between the user or system and the vCenter server. The goal is to prevent unauthorized users from gaining access to critical virtualized resources. The authentication process involves the following key components:

  • User Credentials: A user attempting to access vCenter must provide valid credentials, typically consisting of a username and password.
  • vCenter Server Verification: It checks whether the provided username and password match an existing user account.
  • Token Generation: This token is a temporary access key that grants the user access to the requested resources.
  • Session Establishment: This session provides the user with access to the vCenter interface and its associated functionalities.


Types of vCenter SSH errors

SSH (Secure Shell) is a common protocol used for secure remote access to servers and networking devices, including VMware vCenter. SSH errors can occur for various reasons, often related to authentication, network connectivity, or configuration issues. Here are some types of vCenter SSH errors you might encounter:

  • Authentication Errors: These arise from incorrect credentials, invalid keys, or insufficient permissions.
  • Host Verification Errors: Mismatches in host keys or man-in-the-middle attack suspicions.
  • Connection Issues: Timed-out or refused connections due to network or server problems.
  • Protocol and Version Errors: Incompatibility between client and server SSH protocols.
  • Configuration and Server Errors: Absence of SSH service or misconfigured port settings.

Common Causes of "Too Many Authentication Failures"

The error message "vCenter SSH Too Many Authentication Failures" typically occurs when attempting to authenticate with a remote server, such as SSH, and the server received disconnect from too many authentication failures due to multiple failed attempts. Here are some common causes for this error:

  • Incorrect Credentials: Repeatedly entering incorrect usernames or passwords triggers the error. This could be due to typos, forgetting the correct credentials, or mistaking the password.
  • Network Connectivity Issues: Intermittent network connectivity problems can lead to incomplete authentication attempts, causing the server to interpret them as failed attempts.
  • Account Lockout Policies: Security policies can be set to lock out accounts after a certain number of failed authentication attempts. Once an account is locked, further login attempts are blocked for a predefined period.

How to fix vCenter too many authentication failures

Fixing "Reset Too Many Authentication Failures" issue in vCenter requires a systematic approach to identify and address the underlying causes. Here's a step-by-step guide to help you resolve this problem:

❖ Use a Specific SSH Key for a Specific SSH Server in configuration file

1. Launch or generate the SSH configuration file, found at ~/.ssh/config, utilizing your favored text editor.

2. Integrate a new section dedicated to the desired SSH server connection, employing the subsequent syntax:




3. Preserve the modified configuration file and close it. Subsequently, you can initiate a connection to the SSH server by executing the ssh command with the designated key as stated in the configuration file.

❖ Use a Specific SSH Key in command line

1. In the SSH command, the -i parameter serves to designate the authentication identity (private key) file.

2. Typically, SSH searches for the private key in the user's home directory with filenames id_rsa or id_dsa.

Nonetheless, if the private key resides in an alternate location or has an alternative filename, the -i parameter is employed to define the path to the private key file.

ssh -i ~/keyfile ip address

❖ Increase MaxAuthTries in SSH

1. Click “i” to initiate the editing mode within the document.

2. Once the adjustment of "MaxAuthTries" to 10 is completed, pressing "Esc" is followed by entering ":wq" to store the changes and conclude editing.

3. Execute the command "service sshd restart" or "sudo service sshd restart" to enforce the modifications enacted in the file.


Regular vCenter VM backup against any failures

Despite facing numerous authentication failures in vCenter, ensuring the security and integrity of your virtual environment remains a top priority. However, it is equally critical to safeguard your valuable VM data through regular backups. By shifting your focus towards vCenter VM Backup, you can proactively address the potential risks associated with authentication failures and guarantee the uninterrupted availability and recoverability of your VMs.

Here I would like to introduce you a reliable vCenter VM backup software – AOMEI Cyber Backup. With its comprehensive set of features and user-friendly interface, AOMEI Cyber Backup simplifies the process of safeguarding your virtual machines within the vCenter environment. Additionally, it also provides you with the following benefits:

✦ Agentless Backup: Create complete and independent image-level backup for VMware ESXi and Hyper-V VMs without installing any agent.
✦ Multiple VM Backup: Batch backup large numbers of VMs managed by vCenter Server, or multiple VMs on a standalone ESXi host.
✦ Multiple Storage Destinations: Backup to a local drive, or network destinations like NAS.
✦ Automated Execution: Create backup schedules to automate backups daily, weekly, or monthly.
✦ Restore Entire VM: Restore instant available VMs from any selected restore points to an original or new location.

AOMEI Cyber Backup supports VMware ESXi 6.0 and later versions. Next, I will demonstrate how to quickly backup VMware virtual machines. You can click the button below to try AOMEI Cyber Backup for a 30-day free trial:

Download Free TrialVMware ESXi & Hyper-V
Secure Download

*You can choose to install this VM backup software on either Windows or Linux system.

Backup and restore your VMs with ease via AOMEI Cyber Backup

1. Bind Devices: Access to AOMEI Cyber Backup web client, navigate to Source Device >> VMware >> + Add VMware Device to Add vCenter or Standalone ESXihost. And then click >> Bind Device.


2. Create Backup Task: Navigate to Backup Task >> + Create New Task >> Backup Type >> VMware ESXi Backup and set Task Name, Device, Target, Schedule, and Cleanup as needed.

  • Device: Batch select large numbers of VMs managed by vCenter Server for centralized backup.


  • Schedule (optional): Perform full, differential, or incremental backup, and automate execution according to the frequency you specified.


  • Cleanup (optional): Automatically delete the old backup copies that exceed the retention period you specified.


3. Run Backup: Click Start Backup and select Add the schedule and start backup now, or Add the schedule only.


4. Restore Task: When restoring, you can alsorestore to new locationto create a new VM in the same or another datastore/host directly from the backup, saving the trouble of re-configuring the new VM.



The vCenter authentication process plays a critical role in maintaining the security of your virtualized environment. By requiring valid credentials, generating secure authentication tokens, and establishing encrypted sessions, vCenter ensures that only authorized users can access and manage your virtual machines and resources.

As virtualized environments become increasingly essential in modern IT operations, understanding and implementing robust authentication practices in vCenter is a fundamental step toward safeguarding your infrastructure from unauthorized access and potential threats.

Zelia · Editor
Zelia is an editor from AOMEI Technology.She mainly writes articles about virtual machine. Writing is one of her hobbies and she wants her articles to be seen by more people. In her spare time, she likes to draw and listen to music, and it is a pleasure for her to focus on her own world.