How Do I Suspend a VM?

Suspending a virtual machine (VM) is a convenient way to pause its operation at its current state, allowing for an instant resume exactly where you left off. Unlike powering off or shutting down, suspending saves the VM's entire memory and system state to disk, enabling a rapid restart without the usual boot process.

What is VM Suspension?

VM suspension is akin to putting your physical computer to sleep or hibernate. When you suspend a VM, the hypervisor (like VMware Workstation, VirtualBox, or Hyper-V) captures the entire active state of the VM—including its running applications, open documents, and operating system state—and saves it to a file on your host machine's storage. This process allows you to free up host resources temporarily and then quickly return to your work inside the VM without losing progress.

Key Benefits:

Instant Resume: The VM starts almost immediately, picking up exactly where it was suspended.
Preserves Work: All applications and files remain open and in their last state.
Resource Management: Temporarily frees up CPU and RAM resources on your host machine.

Steps to Suspend a Virtual Machine

The process for suspending a VM is generally straightforward across most virtualization platforms. Here's how it typically works, focusing on common desktop hypervisors like VMware Workstation or Player:

Open Your Virtualization Software: Launch VMware Workstation, VMware Player, VirtualBox, or your preferred hypervisor.
Select the Desired VM: From your library or list of virtual machines, click on the VM you wish to suspend. Ensure the VM is currently running.
Initiate Suspend:
- Via Menu: Go to the "VM" or "Machine" menu and select "Suspend" or "Pause Guest" (terminology may vary slightly).
- Via Toolbar/Buttons: Many virtualization applications provide a "Suspend" or "Pause" button directly in the VM console or toolbar. It often looks like a pause symbol (two vertical lines).
- Close Action: If you attempt to close the VM window while it's running, you'll typically be prompted with options like "Power Off," "Shut Down Guest," or "Suspend." Choose "Suspend."
Wait for Completion: The virtualization software will then save the VM's state to disk. This might take a few moments, depending on the VM's memory size and your host's disk speed.

Once the process is complete, the VM's status will change to "Suspended," and its window may close or display a suspended state indicator.

For more detailed information on managing virtual machines, you can refer to the official documentation for your specific virtualization software, such as VMware Workstation Pro or Oracle VM VirtualBox.

Resuming a Suspended VM

To resume a suspended VM:

Open Your Virtualization Software: Launch the application where your VM is managed.
Select the Suspended VM: Locate the VM in your library; its status should indicate "Suspended."
Start/Resume: Click the "Start" or "Power On" button for that VM. The hypervisor will load the saved state from disk, and the VM will quickly return to its active state exactly as it was when suspended.

Managing and Troubleshooting Suspend States

While suspending a VM is usually reliable, sometimes a suspend operation might get interrupted, or a saved state file (.vmss) can become corrupted. In such cases, the VM might refuse to start, or you may encounter errors. If you need to manually clear a problematic suspend state, you can do so by directly interacting with the VM's files.

When to Manually Clear a Suspend State

You might need to manually clear a suspend state if:

The VM fails to resume correctly from a suspended state.
The VM shows an error or gets stuck when you try to power it on.
You want to force the VM to boot from scratch instead of resuming from a potentially old or unstable suspend point.

How to Manually Clear a Corrupted Suspend State

This process involves deleting the suspend state file and then clearing the reference to it in the VM's configuration file. Follow these steps carefully:

Close Your Virtualization Software: Ensure the application (e.g., VMware Workstation, VMware Player) is completely closed on your host system. This prevents the hypervisor from locking the VM's files or overwriting your changes.
Locate the Virtual Machine's Folder: Navigate to the specific folder on your host machine where the virtual machine's files are stored. This folder typically contains several files related to your VM, including configuration files, virtual disks, and suspend state files.
Delete the Suspend State File: Inside the VM's folder, look for a file with the .vmss extension (e.g., MyVM.vmss). This file contains the snapshot of the VM's memory. Delete this file.
Open the Configuration File: Find the virtual machine's configuration file, which has a .vmx extension (e.g., MyVM.vmx). Open this file using a plain text editor (such as Notepad on Windows, TextEdit on macOS, or any code editor).
Find the checkpoint.vmState Line: Within the .vmx file, search for a line that typically begins with checkpoint.vmState =. This line points to the last saved suspend state.
Remove Content Between Quotation Marks: Carefully delete all content that appears between the quotation marks on this specific line. For instance, if the line reads checkpoint.vmState = "MyVM.vmss", modify it to checkpoint.vmState = "".
Save and Close: Save the changes to the .vmx file and close the text editor.
Restart and Power On: You can now reopen your virtualization software. When you attempt to power on the VM, it should perform a fresh boot, as if it were powered off, instead of trying to resume from the now-cleared suspend state.

Best Practices for VM Suspension

Save Important Work: Always save your work within the VM before suspending, especially if you plan to keep it suspended for an extended period or if your host machine might unexpectedly shut down.
Sufficient Disk Space: Ensure your host machine has enough free disk space to save the VM's memory state, which can be several gigabytes depending on the VM's configured RAM.
Stable Host: Suspending a VM relies on a stable host system. Avoid suspending if your host is under heavy load or might crash.

Suspend vs. Power Off vs. Shut Down

Understanding the differences between these states is crucial for effective VM management.

Feature	Suspend	Power Off	Shut Down (Guest OS)
State Saved	Full memory and system state	None	All applications closed, OS fully exited
Start Time	Instant resume	Cold boot (like a physical computer)	Normal OS boot time
Data Loss	No data loss (unless suspend state corrupted)	Potential data loss if applications not saved	No data loss (applications gracefully closed)
Host Impact	Requires disk space for saved state	No extra disk space needed beyond VM files	No extra disk space needed beyond VM files
Action	Hypervisor-controlled pause	Abrupt cut of power (like unplugging)	Graceful OS shutdown (like Windows/Linux shutdown)
Use Case	Quick pause, temporary resource release	Emergency stop, when graceful shutdown is not possible	Standard, graceful exit; recommended for maintenance