sudo: unable to resolve host — how to fix

sudo: unable to resolve host myserver: Name or service not known

Quick fix: Run hostname to see the name, then add 127.0.1.1 myserver to /etc/hosts (e.g. echo "127.0.1.1 $(hostname)" | sudo tee -a /etc/hosts).

What it means

sudo looks up the machine's own hostname. After changing the hostname (or on some cloud/container images), /etc/hosts no longer contains it, so the lookup fails. sudo still works, but prints the warning and may be slow.

Fix

hostname
cat /etc/hosts

Add the hostname (Debian/Ubuntu use 127.0.1.1 for it):

echo "127.0.1.1 $(hostname)" | sudo tee -a /etc/hosts

Or edit the file and make the line look like:

127.0.0.1   localhost
127.0.1.1   myserver

Changing the hostname properly

sudo hostnamectl set-hostname newname

Then update /etc/hosts to match. On cloud VMs, cloud-init may rewrite /etc/hosts at boot. Set manage_etc_hosts: true in cloud-init config, or edit /etc/cloud/templates/hosts.debian.tmpl.

WSL

WSL regenerates /etc/hosts on start. If the name is missing, check generateHosts in /etc/wsl.conf.

Last updated 2026-10-27.