What is vmx in VMware?

VMware is a popular virtualization platform that allows you to run multiple virtual machines (VMs) on a single physical server. VMWare uses files with the .vmx extension to store the configuration settings and parameters for each virtual machine.

What is vmx in VMware?

The .vmx file defines the virtual hardware components of a VM, including CPU, memory, network interfaces, storage, USB controllers, and more. When you create a new VM in VMware, a .vmx text file is generated which contains details about that VM. Understanding what’s inside the vmx file and how to optimize it is key for efficiently running VMs.

What is in a .vmx File

A vmx file contains details about the virtual hardware, boot options, advanced configuration parameters, and resources allocated to the guest OS. Here are some key sections generally found in a VMware .vmx file:

Virtual Hardware Settings

This section defines components like virtual CPU, memory, network adapters, disk controllers, sound cards, graphics card, USB controller, etc. It controls the virtual hardware environment made available to the guest OS.

Boot Options

The boot options define the boot device order as well as other boot settings like EFI secure boot or enabling boot delay. It decides the boot behavior when powering on the VM.

Advanced Configuration Parameters

These parameters fine-tune and optimize VM performance for factors like memory usage, disk caching, latency sensitivity, TCP/IP stack configuration, and tools integration.

Resource Allocation

Resources like virtual sockets, number of cores per socket, total CPU count, memory size, disk provisioning type, disk shares, network connection types etc. are configured in the .vmx file. These control the quality of resources available to virtual machines.

Editing the .vmx File

While VMware Workstation provides a user interface to edit settings, at times directly modifying the .vmx file becomes necessary.

Here are some common reasons to edit vmx files manually:

  • Troubleshoot VM boot or performance issues
  • Override misconfigured or corrupted VM settings
  • Adjust parameters not available through UI like latency sensitivity
  • Optimize configurations like disk shares, memory reservations etc.
  • Enable/disable experimental or unsupported features
  • Reconfigure VM before importing to other hosts
  • Automate VM deployments across multiple systems

When editing .vmx files manually, few things to keep in mind are:

  • Take backup before making changes
  • Edit using a text editor like Notepad++ and not word processors like MS Word
  • Modification takes effect after next power on in most cases
  • Improper syntax or invalid values can lead to failures or unexpected behaviors

Refer to VMware documentation for valid configuration keys and accepted values to avoid issues.

Importing/Exporting VMs with .vmx Files

VMware .vmx files come handy in importing or exporting virtual machine configurations across environments.

  • Import VMs – The .vmx file contains full configuration so it can be easily imported via VMware Workstation to setup same VM with identical hardware parameters on any host. Just point the import wizard to vmx location.
  • Portable VMs – Combining the .vmx along with .vmdk files enables moving or deploying whole VMs across physical servers via simple file copy without complex migrations. The VM readily boots up on any VMware platform reading .vmx
  • Troubleshooting – Incorrect vmx configurations may lead to failed VM boot or performance lags. By exporting the file and analyzing settings, errors can be identified and fixed quickly.
  • Backups – Regularly backing up the VM’s vmx and vmdk files provides an efficient way to restore VMs to previous known stable states in cases of failures.

The self-contained nature of data within .vmx file makes it indispensable for seamless VM management.

Optimizing .vmx File for Performance

The vmx configuration exposed to VMs significantly impacts efficiency and responsiveness. Here are some tweaks within vmx file to optimize VM performance:

Set Latency Sensitivity

Adding sched.latencySensivity = “high” caters to time-sensitive applications by optimizing interrupt handling.

Disable Swap File

Add sched.swap.derivedName =“” to avoid disk swapping so all guest memory is retained in RAM.

Increase Memory Reservation

Boost reserved RAM for VM using memReserve = “4096” to improve performance consistency.

Isolate CPU

Dedicate specific cores to VM by configuring cpuid.coresPerSocket = “1” and server.cpuidMask = “2” for stable CPU availability.

Partition VM Storage

Break VM disks into multiple .vmdk files using partitions or separate volumes to allow managing storage IOPS independently.

There are many other .vmx tweaks possible to enhance storage, CPU, memory, network I/O for faster VM execution.

Key Takeaway

  • The .vmx file defines all virtual hardware environment and configurations for a VMware virtual machine
  • It controls critical VM parameters – CPU, memory, disks, boot options, devices along with advanced settings
  • Editing the text-based .vmx file assists in troubleshooting issues, changing unsupported features or optimizing VM performance
  • Portable VMs can be created by exporting the self-contained .vmx and .vmdk files to be migrated between hosts
  • Tuning options inside the file like disk shares, latency sensitivity, reservations and partitions boost VM speed


In summary, the VMware .vmx file is integral to manage the virtualization environment defining the identity of a virtual machine. Learning how to optimize and reconfigure the .vmx text file enables tuning the efficiency, reliability and portability of VMs across infrastructures. It expands troubleshooting options when facing VM boot or execution issues. With .vmx editing knowledge virtual machines can be sized, customized and transported to perfectly fit application needs.


Q1: Why am I unable to start my imported VM showing .vmx error?
Validate .vmx file contents using text editor for any syntax errors, unknown keys or invalid values. Rectify issues based on VMware documentation before reattempting power on.

Q2: How to change number of CPUs in an existing VMware virtual machine?
Open related .vmx file and modify numvcpus parameter. Add additional cores in cpuid.coresPerSocket. Reboot VM to activate new CPU count.

Q3: What is the easiest way to move VMs between ESXi hosts?
Export the VM’s .vmx and .vmdk files. Copy both files to target host and register VM using the Import wizard. Retains full configuration portability.

Q4: Can I configure my VM’s virtual hardware without the Workstation interface?
Yes, entire VM hardware like disk, CPU, network, graphics is controlled through directives within the .vmx file itself. Modify as per documentation to customize without UI.

Q5: Where is the .vmx file located on my local machine?
For VMware Workstation, the .vmx files reside in subfolders under C:\Documents and Settings{user-name}\My Documents\My Virtual Machines\

Q6: If I delete the .vmx file will I lose my VM?
Yes, removing .vmx deletes VM identity and hardware metadata. Associated .vmdk files retain only storage data. Must import .vmdk into new VM after recreating .vmx to recover.

Q7: How can I tell VMware to use specific physical NIC for my VM?
Configure virtual network adapter in .vmx file using ethernetX.virtualDev = “vmxnet3” and ethernetX.networkName = “Network Adapter Name” where X=0,1..

Q8: Can I run VMware VM without an operating system?
No OS is required. Set firmware in .vmx as firmware = “efi” and boot VM. Gets you into EFI shell for testing or troubleshooting VM hardware.

Q9: Is too many VMs per server slowing down performance?
Yes, excessive VMs contend for fixed resources. Tune .vmx in each VM to lower reservations,shares, isolate CPUs & adapters. Also partition storage across more disks.

Q10: What is the easiest way to duplicate or backup VM configuration?
Simply copy the source VM’s .vmx and .vmdk files to new location. Register the vmx in Workstation to instantiate same VM with identical configuration.

Q11: Can I adjust my VMware virtual machine to utilize more physical CPU cores?
Yes, directly edit numvcpus,  cpuid.coresPerSocket and server.cpuidMask in .vmx file to tune virtual sockets/cores spanning host CPU. Takes effect on reboot.

Q12: What is the file extension for virtual disk files in VMware?
The primary disk file for VMware virtual machines uses the .vmdk (Virtual Machine Disk) file extension. This contains full virtual hard disk data.

Q13: Can I rename my VM {vmname}.vmx file safely?
No, the vmx filename must match internal VM name referenced from configuration. Changing .vmx name will break VM execution and fail to power on.

Q14: How to correctly upgrade the virtual hardware version of an existing VM?
Edit .vmx parameter virtualHW.version value to latest supported by host ESXi/Workstation edition. Older VMs can limit features until upgraded.

Q15: What VMware file locks the .vmx configuration file?
The VMX process starts when powered on which holds an exclusive lock on .vmx preventing external edits. Use vim-cmd vmsvc/getallvms to identify powered on VM process.

Q16: How do I convert VMware Workstation VM for use on VMware ESXi?
Install VMware Workstation to ESXi, then cross-convert the .vmx and .vmdk files transferring them to the ESXi datastore for registration.

Q17: Which directory stores the configuration files for VMware based VMs?
VMware VMs store all related config files – .vmx, .nvram, .vmdk etc within a subfolder matching VM name under VM folder location configured for the host.

Q18: Instead of a new VM can I direct an existing VMware VM to boot from ISO?
Yes, edit .vmx adding lines ‘firmware = “efi”’ and ‘efi.nvram = “[path to efi file]”’ to directly boot VM into a UEFI mode from ISO without guest OS.

Q19: What is the easiest way to change allocated CPUs or memory for a VM?
Edit numvcpus, coresPerSocket and memsize mb values under respective sections in .vmx file from a text editor. Update resources without UI assistance.

Q20: What VMware file defines the guest OS type to be installed?
The .vmx contains guestOS = “name” in the file header indicating intended guest OS. Change this entry to alter guest for Linux, Windows or other VMware supported OS.

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