A Fix for “sudo: unable to resolve host” in WSL

The Problem

If you’ve used WSL for any amount of time, you might have noticed that anytime that you attempt to run a command with sudo, there’s a slight delay followed by an error that your hostname can’t be resolved and then the usual prompt for your password:

$ sudo apt-get update
sudo: unable to resolve host MacBookWin
[sudo] password for jim:

While it’s not the end of the world that you see this little warning, that small delay can get to be a little annoying each time you want to run a command with elevated privledges.

The issue is that when WSL is installed and setup, your hostname is not included in your hosts file, which you can see by viewing your hosts file:

$ cat /etc/hosts
127.0.0.1 localhost

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

The Solution

Luckily the solution is very simple, you just need to edit your hosts file to include your hostname by doing the following:

Check Your Hostname

While not 100% necessary if already know your hostname in WSL (it should be the same as your Computer Name in Windows), you can see your hostname by typing hostname:

$ hostname
MacBookWin

Edit Your Hosts File

Open your hosts file in nano:

sudo nano /etc/hosts

Scroll down to 127.0.0.1 localhost and add your hostname after localhost. Your hosts file should now look like this (with your hostname from above instead of MacBookWin):

127.0.0.1 localhost MacBookWin

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Now you just need to hit Ctrl+O to save the file and Ctrl+X to exit nano.

Restart Bash

Now as a good measure, close out of Bash, start it up and try to use sudo:

$ sudo apt-get update
[sudo] password for jim:

If you don’t see that line complaining that your hostname can’t be resolved, you’re good to go!