Cannot use WSL anymore

I cannot use WSL(Ubuntu on Windows). When I run bash in CMD, I will get an error

Error:0x8007001f

But I can use it normally before some days, I don't know which my operation result in this problem. Please help me out.

0x8007001f appears to be an update error of some description.

If you have the Fall Creators Update have you may need to install Ubuntu from the Windows Store.

Microsoft Store: Ubuntu

If you are missing the bash.exe command then apparently you need to set up the default distribution (as mentioned by nightwolfz in that thread):

You can solve it by checking which distro's are installed with:

wslconfig.exe /l

and then setting default distro with:

wslconfig.exe /s Ubuntu

Enjoy fixed bash.exe !

This is necessary as you can now have multiple different distributions installed.