Fix DNS resolution in WSL2

wsl2_200915_fix_dns_resolution.md

Error

$ sudo apt-get update
Err:1 http://archive.ubuntu.com/ubuntu focal InRelease
Temporary failure in name rerolution

$ host google.com
;; connection timed out; no servers could be reached

Solution

The /etc/resolv.conf is the main configuration file for the DNS name resolver library. It was automatically generated by WSL. Some time there was a problem with that DNS.

1. To stop automatic generation of resolv.conf, add the following entry to /etc/wsl.conf:

$ sudo cat << EOF > /etc/wsl.conf
[network]
generateResolvConf = false
EOF

2. In a cmd/powershell window, run:

> wsl --shutdown

or:

> wsl --terminate <Distro>

3. Restart WSL
4. Create a file: /etc/resolv.conf. If it exists (even a link), replace existing one with new file.

sudo cat << EOF > /etc/resolv.conf
# Use one or many DNS servers you like
# nameserver 192.168.1.1
nameserver 8.8.8.8
nameserver 1.1.1.1
EOF

5. Shutdown and restart WSL again.

Still not working

cmd/powershell as admin:

> wsl --shutdown  
> netsh winsock reset  
> netsh int ip reset all  
> netsh winhttp reset proxy  
> ipconfig /flushdns  

Restart Windows.

Ref:

• Colten Krauter: Fix DNS resolution in WSL2
• RedHat: Chapter 27. Manually configuring the /etc/resolv.conf file
• StackExchange: How do I set my DNS when resolv.conf is being overwritten?
• TechMint: How To Set Permanent DNS Nameservers in Ubuntu and Debian
• rescenic: No network connection in any distribution under WSL 2

I figured out, I can leave the defaults inside WSL2 (let /etc/wsl.conf default and automatically create resolv.conf).
I simply have to reset the Windows settings like you described here, and then it works again....