VMware Tools installation fails with error "The VMware Tools upgrade operation was canceled. vix error code = 21004"

Products

• VMware vSphere ESXi

Issue/Introduction

When attempting to install or upgrade VMware Tools from the vCenter vSphere Client:

• Right-click VM → Guest OS → Install VMware Tools (or Upgrade VMware Tools)

The operation fails with the following error,

    mountInstaller failed!

    The VMware Tools upgrade operation was canceled.
    vix error code = 21004
    The VMware Tools installation was canceled

In the virtual machine vmware.log, entries similar to the following are observed:

Case 1 – Missing windows.iso hash file windows.iso.sha

ToolsISO: open of /vmfs/volumes/<datastore-uuid>/locker/packages/vmtoolsRepo/vmtools/windows.iso.sha failed: Could not find the file
ToolsISO: Unable to read hash file /vmfs/volumes/<datastore-uuid>/locker/packages/vmtoolsRepo/vmtools/windows.iso.sha
[msg.cdromImage.sigFailed] The ISO image signature could not be verified
CDROM-IMG: Tools ISO verification failed
TOOLS INSTALL cancelling tools installation (error=5)
toolsInstallManager.lastInstallError = "21004"

 

Case 2 – Missing windows.iso signature file windows.iso.sig

After restoring the .sha file, the issue may persist with the following log entries:

ToolsISO: open of /vmfs/volumes/<datastore-uuid>/locker/packages/vmtoolsRepo/vmtools/windows.iso.sig failed: Could not find the file
ToolsISO: Unable to read signature file '/vmfs/volumes/<datastore-uuid>/locker/packages/vmtoolsRepo/vmtools/windows.iso.sig'
[msg.cdromImage.sigFailed] The ISO image signature could not be verified
CDROM-IMG: Tools ISO verification failed
TOOLS INSTALL cancelling tools installation (error=5)
toolsInstallManager.lastInstallError = "21004"

 

 

Environment

vSphere ESXi 8.x

vSphere ESXi 9.x

Cause

vSphere ESXi performs integrity and signature verification before mounting the VMware Tools ISO.

This process requires the following files to be present in the Product Locker /vmfs/volumes/<datastore-uuid>/locker/packages/vmtoolsRepo/vmtools/ (or /locker/packages/vmtoolsRepo/vmtools/),

• windows.iso
• windows.iso.sha (hash file)
• windows.iso.sig (signature file)

If either the .sha or .sig file is missing:

• ESXi cannot verify the ISO
• The ISO mount operation fails
• VMware Tools installation is canceled with vix error code 21004

Resolution

Restore both the missing hash and signature files from a healthy ESXi host.

1. Verify ISO consistency between hosts
   
   Before copying any files, confirm that the the windows.iso file on both the source and affected ESXi hosts is identical by sha1sum or comparing file size.

   sha1sum /locker/packages/vmtoolsRepo/vmtools/windows.iso

   or

   ls -l /locker/packages/vmtoolsRepo/vmtools/windows.iso

   Ensure the hash values or file sizes are the same.
   
   Important:
   Do not copy .sha or .sig files if the windows.iso files differ, as this will result in continued verification failure.

2. Verify files on a healthy host 

   ls /locker/packages/vmtoolsRepo/vmtools/windows.iso

   Expected files:

   windows.iso
   windows.iso.sha
   windows.iso.sig

   
   
3. Copy missing files to the affected host
   
   Use scp or sftp to copy the files windows.iso.sha and windows.iso.sig to the affected host.
   
   
4. Retry VMware Tools installation
   
   Right-click VM → Guest OS → Install VMware Tools (or Upgrade VMware Tools)
   
   The ISO should mount successfully and installation will proceed normally.
   
   
   

 

 

Additional Information

• Both .sha and .sig files are required. Copying only one file will not resolve the issue.

• Ensure the windows.iso file is identical between hosts before copying verification files.

• No reboot is required:

  • ESXi host restart is not required

  • Virtual machine reboot is not required