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Updated Ship WSL 2 Linux Kernel (markdown)

Canhua Li 2020-06-20 20:32:43 -07:00
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Ship-WSL-2-Linux-Kernel.md

@ -9,6 +9,7 @@ The whole serving story is divided into three steps:
2. Remove Linux kernel from Windows. When you see `WSL 2 requires an update to its kernel component. For information please visit https://aka.ms/wsl2kernel`, that means you are in this step.
3. Linux kernel update is delivered to your machine automatically by Microsoft Update.
---
## Windows Subsystem for Linux Update (MSI installer)
@ -38,11 +39,30 @@ If Linux kernel is removed from Windows image, you will see this error message:
---
## Deliver Kernel by Microsoft Update
### Design of Kernel update
Kernel is delivered by Microsoft Update, and two version of kernels are kept in tools: `kernel` and `kernel.rollback`. You are able to rollback to previous version by `wsl --update --rollback`, but
wsl.exe doesn't provide public interface to revert the rollback. It's by design.
TBD
When rollback happens, it's assumed that this version is bad and user should not pickup this version again.
Assume Microsoft shipped three versions of version:
**A(.104) -> B(.121) -> C(.1xy)**
User hits problem on version B(.121), then user rolled back to A(.104). So no public interface is provided for you to revert the rollback. Here is the status of kernel:
| kernel | kernel.rollback |
|---|---|
| B(.121) | A(.104) |
When bug fix for B is ready and C is shipped, user picks up C automatically by Windows Update. Since B is assumed bad and A is good, user is not allowed to rollback to B too but A. Here is the actual mapping after user updates to C:
| kernel | kernel.rollback |
|---|---|
| C(.1xy) | A(.104) |
version B(.121) is dropped because it's assumed bad and it's only allowed to rollback from C to A(.104)
---
## Troubleshooting
## Troubleshooting and How to
#### `This update only applies to machines with the Windows Subsytem for Linux`
see Pre-Check Step
@ -63,3 +83,26 @@ Not matter what reason, there is no `%SystemRoot%\system32\lxss\tools\kernel` ex
- `msiexec /a "wsl_update_x64.msi" /qb TARGETDIR="C:\temp"`
- copy the kernel file from C:\temp to `%SystemRoot%\System32\lxss\tools`
### How to rollback kernel
MSI installer keeps two version of kernel, if you find `kernel.rollback` in tools, then you are able to rollback to an old version of kernel.
`
dir %SystemRoot%\system32\lxss\tools\kernel*
`
You can rollback the kernel with below command which requires admin permission.
```
wsl.exe --update --rollback
wsl --shutdown
```
Please note that `--shutdown` stops both WSL 1 and WSL 2 instances.
After `wsl --update --rollback`, the running instance doesn't pick up the kernel immediately, you have to save your work, then shutdown and restart the Linux.
### How to revert the kernel rollback
wsl doesn't provides public interface for you to revert the rollback, but you still be able to do it manually:
```
deleting RollbackKernel in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Lxss
wsl --shutdown
```