What is .vmx file in virtual machine?

by
What is .vmx file in virtual machine

A .vmx file is a configuration file that defines the settings for a virtual machine in VMware virtualization products like VMware Workstation, VMware Player, VMware Fusion, and VMware ESXi. It contains details about the virtual machine’s virtual hardware, number of processors, memory allocation, network connection, storage devices, etc.

What is the purpose of .vmx file?

The main purposes of the .vmx file are:

  • It describes the virtual hardware configuration of the virtual machine.
  • It specifies the virtual hardware devices like disk drives, network adapters, memory size, number of vCPUs etc.
  • It contains settings for BIOS, boot order, power management.
  • It sets configuration options for remote access, sharing folders between host and guest.
  • It determines the guest operating system type and version.

In summary, the .vmx file defines the virtual hardware environment that the virtualization software emulates for that virtual machine. It is an essential configuration file needed to run the virtual machine.

Where is the .vmx file located?

The location of the .vmx file depends on the VMware product:

  • In VMware Workstation and VMware Player, it is stored in the virtual machine folder, alongside the .vmdk disk image files.
  • In VMware Fusion, it is inside the .vmwarevm bundle file that contains the virtual machine.
  • In ESXi, it is located in the VM’s configuration directory in the datastore.

The .vmx file always resides with the other files that make up the virtual machine. For example, in Windows the default path is C:\Documents and Settings\username\My Documents\My Virtual Machines\vmname\vmname.vmx

What does a .vmx file contain?

A .vmx file is a text file that contains configuration keys or directives surrounded by double quotes, along with values assigned to them. Some of the common keys in a VMware .vmx file are:

  • .encoding – specifies file encoding format
  • config.version – version of virtual hardware
  • virtualHW.version – virtual hardware type (4, 7, 8 etc)
  • numvcpus – number of virtual CPUs
  • memsize – memory size in MB
  • scsi0.present = “TRUE” – add SCSI controller
  • ide1:0.present = “TRUE” – attach IDE disk
  • ethernet0.present = “TRUE” – enable network adapter
  • ethernet0.connectiontype – network connection type
  • ethernet0.addressType – MAC address type
  • ethernet0.vnet – virtual network
  • uuid.bios – BIOS unique ID
  • checkpoint.vmState – saved state of VM
  • tools.syncTime – sync time with host
  • snapshot.x.uuid – UUID of snapshot

Overall the .vmx file has sections for the VM identity, storage, memory, CPU, boot options, networks, remote access, time synchronization and other features.

How to edit the .vmx file?

The .vmx file is a simple text file that can be opened and edited in any text editor like Notepad, Vim etc. However, proper care must be taken while editing it manually because any mistakes could corrupt or break the virtual machine.

Here are some tips for editing .vmx files:

  • Make a backup copy before editing
  • Open the .vmx file in a text editor like Notepad
  • Edit the values or add new keys as required
  • Save the changes back to the .vmx file
  • Double check the syntax to ensure no typos or format errors
  • Change one setting at a time and test
  • After editing, power off the VM before restarting it

Alternatively, tools like PowerCLI and VMware OVF tool can programmatically edit the .vmx files for automation tasks. Overall use caution when manually editing the file.

Why edit the .vmx file?

Some common reasons for manually editing the .vmx file are:

  • Increase memory, CPUs of an existing VM
  • Change MAC address of a network adapter
  • Enable or disable a virtual hardware device
  • Modify virtual disk settings
  • Set parameters not exposed through GUI
  • Troubleshoot VM issues

Instead of recreating a VM from scratch, the .vmx file can be modified to quickly reconfigure the virtual hardware settings as per requirements.

What are the key points to note when editing .vmx files?

Following are some important points that need attention when manually editing .vmx files:

  • Strictly adhere to the syntax – the .vmx file format is rigid
  • Spell check keys and values – a minor typo could break the VM
  • Match data types – using a string value for an integer key will fail
  • VM must be powered off before editing – changing .vmx on a running VM is not possible
  • Validate after editing – check logs and errors after restarting
  • Edit one setting at a time – changing multiple settings together makes troubleshooting difficult
  • Check compatibility – some settings may not work on older VM hardware versions
  • Mind the limits – cannot exceed maximum vCPUs, memory supported by virtualization host

Careful editing following VMware .vmx documentation helps avoid mistakes that could cause boot failures or crashes.

What are some common .vmx file errors?

Some frequent errors encountered while incorrectly modifying .vmx files are:

  • Typos and spelling mistakes in key names like “memry” instead of “memsize”
  • Missing double quotes around string values like vmname
  • Setting a key to an incorrect data type like assigning a string to a boolean key
  • Specifying invalid or unsupported hardware devices
  • Increasing vCPUs or memory beyond host limits
  • Syntax errors – missing commas, equals sign, semicolons etc
  • Incorrect VM version referenced that doesn’t match virtual hardware
  • Non-contiguous lines – forgetting to terminate a previous line

VMware logs error messages on encountering malformed .vmx files and fails to power on the VM. Checking logs helps debug the exact issue.

What are best practices for editing .vmx files?

Here are some best practices to follow when modifying .vmx configuration files:

  • Maintain proper backups – take backup of the original .vmx file before editing
  • Make changes incrementally – edit one parameter at a time
  • Record changes made – keep notes on keys modified and old/new values
  • Adhere to formatting rules – mind the quotes, commas, casing, spacing
  • Validate syntax – double check for errors, use tools like XSD validator
  • Test thoroughly – verify changes and functionality work as expected
  • Restart VM after editing – ensure VM is powered off before applying .vmx changes
  • Consult documentation – refer VMware .vmx spec for valid keys and values

Following best practices reduces chances of mistakes and data loss. Proper testing also confirms updates work correctly.

Can I delete .vmx file?

Deleting the .vmx file renders the virtual machine unusable. Without the .vmx configuration, the VM cannot power on since the hypervisor has no information on the virtual hardware settings.

However, the other VM files like .vmdk disks can still be recovered and reused if the .vmx is deleted. A new .vmx can be recreated with appropriate hardware configuration to restore access to the existing virtual disks.

So in summary, yes the .vmx can be deleted but it will make that VM non-functional until a new .vmx file is provided.

What happens if I delete .vmx file?

Here is what happens if the .vmx configuration file is accidentally deleted:

  • The virtual machine will disappear from the inventory in Workstation/Fusion
  • Any power on operation will fail with errors
  • The VM’s storage files like .vmdk will still be present
  • A new .vmx file has to be recreated with same config to reuse the disks
  • All current VM state is lost – memory, devices, snapshots etc
  • Virtual hardware details will have to be re-specified in new .vmx

So the VM will become unusable, however no critical data is lost since the disks can be reassociated once the .vmx file is restored.

How to recreate .vmx if accidentally deleted?

If the .vmx file goes missing, follow these steps to recreate it:

  1. Locate the VM’s folder containing its .vmdk/.nvram files
  2. Create a new text file named vmname.vmx in that folder
  3. Add the correct .encoding, config version in the .vmx file
  4. Specify virtual hardware details like CPU, memory, disks etc
  5. Reference the existing .vmdk files
  6. Save and close the new .vmx file
  7. Register the VM in Workstation/Fusion by locating the .vmx
  8. Power on VM to test – it should boot from disks

The key is recreating a .vmx with identical hardware details as the original. Proper reconfiguration allows the VM to access its existing disk files.

What are some sample .vmx files?

Here are some sample excerpt snippets from .vmx files with common configuration settings:

Minimal .vmx

.encoding = "UTF-8"
config.version = "8"
virtualHW.version = "7" 
numvcpus = "2"
memsize = "1024"
ide1:0.present = "TRUE"
ide1:0.fileName = "disk.vmdk"
ethernet0.present = "TRUE"

.vmx with advanced networking

ethernet0.virtualDev = "vmxnet3"
ethernet0.addressType = "generated"
ethernet0.wakeOnPcktRcv = "FALSE"
ethernet0.uptCompatibility = "TRUE"
ethernet0.vnet = "vnet-nat"
ethernet0.TsoEnable = "TRUE"
ethernet0.OffloadLso = "TRUE"

.vmx with cd-rom drive

ide1:0.present = "TRUE" 
ide1:0.fileName = "disk.vmdk"
ide1:1.present = "TRUE"
ide1:1.deviceType = "cdrom-image"
ide1:1.startConnected = "TRUE"
ide1:1.autodetect = "TRUE"

These examples showcase some commonly used .vmx directives to configure CPU, RAM, disks, NICs etc.

Conclusion

The .vmx configuration file is crucial for defining and running virtual machines in VMware environments. It specifies the complete virtual hardware details, provides the virtualization layer critical information needed to emulate the VM hardware and boot the guest OS. Care must be taken while manually editing the file since errors could lead to failures in powering on the VM. Following best practices like regular backups, small incremental changes, and testing can help modify .vmx files safely.

Leave a Comment