WSL Bash doesn't start

Try to do a full reboot of Windows10, hold Shift, and click “Restart.”

Normal reboot/shutdown action in the start menu will not shutdown Windows 10 fully, for the “fast boot” mechanism saves memory from the last session. The other answer mentioned changing system settings which make Windows 10 doing a full reboot, it works, but unnecessary.

By holding the Shift key and click the “Restart” in the start menu, Windows 10 will go into advanced restart mode, choose “Shutdown” from the menu. Then start normally again.

As discussed on https://github.com/Microsoft/WSL/issues/849 by user imkimchi the steps for solving this issue are:

1. Run windows + R
2. type SystemPropertiesAdvanced
3. click settings in performance group
4. In advanced tab, click Change under Virtual Memory and deselect the automatically manage paging file size for all drives
5. Select custom size and enter 800 for initial size, 1024 for maximum size.
6. Apply changes and restart.