Learn how to quickly fix the common ‘sudo: unable to resolve host’ error in Ubuntu by properly configuring your /etc/hosts file. This guide provides a detailed step-by-step solution.

How to Fix ‘sudo: unable to resolve host’ Error in Ubuntu

Encountering the sudo: unable to resolve host error in Ubuntu can be frustrating. This error typically occurs because the hostname is not correctly mapped in the /etc/hosts file. Here’s how you can resolve this issue with a simple edit.

Error Message

When you try to use sudo, you might see an error message like this:

ubuntu@ip-172-27-99-13:~$ sudo bash
sudo: unable to resolve host ip-172-27-99-13

Why This Happens

This error occurs because the system cannot map the IP address to the hostname specified. This mapping is usually defined in the /etc/hosts file. Without the correct entry, sudo commands fail to resolve the hostname, resulting in the error.


To fix this, you need to add the correct hostname entry to your /etc/hosts file. Follow these steps:

Step 1: Open the /etc/hosts File

First, open the /etc/hosts file in a text editor with root permissions. You can use nano, vim, or any editor of your choice. Here’s how to open it with nano:

sudo nano /etc/hosts

Step 2: Add the Hostname Entry

Look for the following line: localhost

Below this line, add your IP address and hostname. For example: localhost ip-172-27-99-13

Replace with your actual IP address and ip-172-27-99-13 with your hostname.

Step 3: Save and Close the File

After making the changes, save the file and exit the editor. In nano, you can do this by pressing Ctrl + X, then Y, and Enter.

Step 4: Verify the Changes

To ensure the changes have taken effect, you can open the /etc/hosts file again and check if the new entry is there. You can also try running the sudo command again to see if the error is resolved.

ubuntu@ip-172-27-99-13:~$ sudo bash

If the error message no longer appears, you have successfully resolved the issue.


By correctly configuring the /etc/hosts file, you can resolve the sudo: unable to resolve host error in Ubuntu. This simple fix ensures your system can map the hostname to the IP address, allowing sudo commands to function correctly.

For more tips and troubleshooting guides on Ubuntu and Linux, stay tuned to my blog!