Search the VMware Knowledge Base (KB)
View by Article ID

Troubleshooting virtual machine console and MKS issues in the vSphere Client (749640)

  • 196 Ratings
Language Editions


  • When you try to connect to a virtual machine console from vCenter Server, you see these errors:

    • Error connecting: Host address lookup for server <SERVER> failed: The requested name is valid and was found in the database, but it does not have the correct associated data being resolved for Do you want to try again?
    • Error connecting: cannot connect to host <host>: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. Do you want to try again?
    • Error connecting: You need execute access in order to connect with the VMware console. Access denied for config file.
    • Unable to connect to MKS: failed to connect to server IP:903.

      Note: Looking at the virtual machine logs (vmware.log), errors with the console will appear as MKS (Mouse,Keyboard,Screen).

  • You cannot open a remote console to a virtual machine.
  • Virtual machine console is black (blank).
  • The VMware vSphere Client console tab session may time out or disconnect while in use.
  • Migration of virtual machines using vMotion fails.
  • This issue may affect a single ESXi/ESX host. If the virtual machines are moved to another ESXi/ESX host, you may be able to connect to the console without issues.
  • This issue may occur if you try to connect to the console using the VMware vSphere Client connected directly to the ESXi/ESX host or to vCenter Server.


This issue may occur if your network contains a firewall between the ESXi/ESX host and the vSphere Client.

Validate that each troubleshooting step below is true for your environment. The steps will provide instructions or a link to a document, for validating the step and taking corrective action as necessary. The steps are ordered in the most appropriate sequence to isolate the issue and identify the proper resolution. Do not skip a step.


Follow these troubleshooting steps:
  1. Log in to vCenter Server directly through Terminal Services or a Remote KVM and attempt a connection using the vSphere Client from this system. If this method works, a firewall may be preventing the console from connecting.

  2. Configure your firewall to allow communications between the ESXi/ESX host and the workstation running the vSphere Client. For more information, see Testing port connectivity with Telnet (1003487) and TCP and UDP Ports required to access VMware vCenter Server, VMware ESXi and ESX hosts, and other network components (1012382).

    Note: If port 903 is not open or cannot be opened in your environment, enable the vmauthd proxy. This forces remote console communication to be sent on port 902 on the Service Console, instead of 903. By enabling this setting there may be degradation in the performance under heavy usage while communicating to the ESXi/ESX host service console.

     Note: In ESXi 4.x, 5.x and 6.0, vmauthd.server.alwaysProxy is, by default, set to true.

    To enable the proxy:

    1. Log into the ESX host's service console as root.
    2. Open /etc/vmware/config using a text editor.
    3. Add this line to the file:

      vmauthd.server.alwaysProxy = "TRUE"

    4. In ESX, run this command to restart xinetd:

      service xinetd restart

  3. Verify the ESXi/ESX firewall policy:

  4. Verify that the ESXi/ESX host and the workstation running the vSphere Client are correctly synced to an NTP service. This is required to satisfy SSL handshaking between the vSphere Client or and the ESXi/ESX host. For more information, see Verifying time synchronization across an ESXi/ESX host environment (1003736).

  5. DNS problems are a common cause of virtual machine console problems. Verify name resolution in your environment. For more information, see:

  6. After verifying DNS, open a command prompt on the vSphere Client machine and run these commands:

    ipconfig /flushdns
    ipconfig /registerdns

  7. Ensure that the VMware ESXi/ESX host has enough disk space in /var and other required partitions. For more information, see Investigating disk space on an ESX or ESXi host (1003564).

  8. Verify that the permissions for the virtual machine's .vmx file are set correctly. To set the permissions, run the command:

    chmod 755 full_path_to_virtual_machine.vmx

  9. Confirm the ESX\ESXi host Gateway is configured correctly.  For more information see  Changing the default VMkernel gateway interface for a network when there are multiple VMkernel ports on the same subnet (2043784).

  10. (ESX only) If your ESX host has more than one service console configured, verify that they are not on the same network. For more information, see ESX 4.x hosts lose network connectivity when multiple service console interfaces are configured on subnets that use DHCP IP addresses (1010828).

  11. (ESX only) Check if the Service Console IP is routing traffic to the workstation running vCenter Server. For more information on configuring the Service Console Gateway, see Changing the IP address, default gateway, and hostname of the Service Console in ESX (4309499).
If the issue still exists after trying the steps in this article:

Additional Information:

For translated versions of this article, see:


cannot-view-console  view-vm-console-fails  vm-console-appears-blank

This Article Replaces


Update History

12/13/2011 - Added ESX only step 2-d 01/10/2012 - Added a note that Proxy is by default set to true in ESXi4.X and 5.X. 10/16/2012 - Added ESXi 5.1 to Products

Request a Product Feature

To request a new product feature or to provide feedback on a VMware product, please visit the Request a Product Feature page.


  • 196 Ratings

Did this article help you?
This article resolved my issue.
This article did not resolve my issue.
This article helped but additional information was required to resolve my issue.

What can we do to improve this information? (4000 or fewer characters)

Please enter the Captcha code before clicking Submit.
  • 196 Ratings