vmIdleTimeout has no effect

[Seeky90]

Version

Version 10.0.22000.739

WSL Version

• WSL 2
• WSL 1

Kernel Version

5.10.102.1

Distro Version

Ubuntu 20.04

Other Software

No response

Repro Steps

Into %userprofile%/.wslconfig add:
[wsl2] vmIdleTimeout=-1
in order to completely disable the timeout.

In Powershell run
wsl --shutdown

Start WSL by opening a Terminal.
Close the Terminal so that nothing is running.

Check the current state of the machine by running in powershell:
wsl --list --verbose

It should show STATE Running.

Expected Behavior

Check again, after for example 5 minutes.
It should show STATE Running.

Actual Behavior

Check again, after for example 5 minutes.
It shows the STATE Stopped.

Diagnostic Logs

#8642

[NotTheDr01ds]

I was thinking the same thing for most of today, but believe it or not, it appears to be working as intended. The documentation wording on this feature is accurate, but confusing:

key	value	default	notes
vmIdleTimeout	number*	60000	The number of milliseconds that a VM is idle, before it is shut down. Only available for Windows 11.

Technically, it should say "the VM", because there's only one WSL2 virtual machine running.

The confusion is that this refers to the managed VM running WSL2 itself, not the WSL2 distribution/container/instance.

There are two timers that are in play here:

• The first timer is how long a WSL instance is idle before it is terminated. Think of this as a wsl --terminate <distro> that occurs when there are no more running processes in it other than init. This is non-configurable, but Add the ability to change the timeout period of a WSL instance #6782 is a feature request for the ability to configure it. As far as I can tell, this is hard-coded at about 15 seconds.

  This has been around since shortly after WSL1 was launched 6 years ago. It occurs for both WSL1 and WSL2 instances.

• The second timer is specific to the WSL2 managed (as in, we can't see it or interact with it, for the most part) VM. This is a single shared VM, which is why I say it would be more accurate to call it *"the VM" in the docs. Even after an instance is terminated, the WSL2 VM continues to run and consume memory.

  A wsl --shutdown essentially terminates this virtual machine (and presumably some other activities).

  You can see this by looking for several processes in the task manager:

  • Vmmem: vmmem.exe
  • Virtual Machine Worker Process: vmwp.exe

  These will show up when you first run a WSL2 instance (which starts the VM) and will go away when the VM is shutdown (either via vmIdleTimeout or wsl --shutdown)

  You can also see the VM start up and shut down in the Event Viewer under Applications and Services Logs -> Microsoft -> Windows -> Hyper-V-Worker -> Admin.

  The vmIdleTimeout is specific to the VM, and that timer starts once all WSL2 distributions/instances/containers have terminated.

So once you exit the last WSL2 VM, assuming no other processes are running in the background:

• A 15 second timer starts, after which the instance itself is terminated
• Then, once the last instance is terminated, the "idle" state timer begins. 60 seconds (by default) after this, the WSL2 VM will shut down.

So setting vmIdleTimeout=-1 will simply keep the VM, but not the instance, running.

Side note: You can also watch the VM shut down if you turn on debugConsole=true.