On all my Ubuntu on Windows installs to date I’ve initially got a sudo: unable to resolve host [PCNAME] error when running a command with sudo.

The problem is that, although the PC name has been added to /etc/hostname, an entry for it has not added to /etc/hosts.

The default /etc/hosts seems to just contain an entry for localhost on 127.0.0.1.

It also needs an entry for [PCNAME] on 127.0.1.1, where [PCNAME] is the value found in /etc/hostname.

NB Modifying files inside of %localappdata%\lxss from Windows is not supported in WSL. It seems you can just about get away with editing /etc/hosts in Notepad but not Notepad++, otherwise you’ll see an Error 0x80070490 when trying to run Bash from the Command Prompt and a rapidly closing window if you try and run it from Start.

TL:DR The best way of resolving this is to delete /etc/hosts and the next Bash session will autogenerate a file with the correct contents.