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How to update readonly hosts file?

How to Update a Read-Only Hosts File on different OS

How to update readonly hosts file?

While trying to edit the read-only hosts file on a Mac, you may see the following message and find that you cannot save your changes:


"hosts" [readonly] 13L, 403B

This article explains what this message means, why the hosts file is read-only, and how you can safely edit and save it with the proper permissions.

Explanation of Each Part

  • hosts – The name of the file you are editing.
  • [readonly] – The file is opened in read-only mode, so changes cannot be saved without elevated permissions.
  • 13L – The file contains 13 lines.
  • 403B – The file size is 403 bytes.

Why Is the Hosts File Read-Only?

The hosts file is a critical system file used to map hostnames to IP addresses before DNS resolution occurs.

Default locations:

  • macOS / Linux: /etc/hosts
  • Windows: C:\Windows\System32\drivers\etc\hosts

Because this file can affect network behavior and security, operating systems protect it and require administrator (root) privileges to modify.

How to Edit the Read-Only Hosts File

macOS / Linux

Use sudo to open the file with elevated permissions:


sudo vim /etc/hosts

If you prefer a simpler editor:


sudo nano /etc/hosts

After editing, save and exit the editor. Your changes will be applied immediately.

Windows

  1. Search for Notepad (or your preferred editor).
  2. Right-click and choose Run as administrator.
  3. Open the file:
    C:\Windows\System32\drivers\etc\hosts

Once opened with admin privileges, you can edit and save the file normally.

Common Use Cases for Editing the Hosts File

  • Pointing a domain to 127.0.0.1 for local development
  • Testing staging environments
  • Blocking unwanted domains
  • Debugging DNS-related issues

Important Notes

  • Always keep a backup before editing system files
  • Incorrect entries can break network connectivity
  • No reboot is required after editing the hosts file

I hope this helps! Feel free to comment if you have questions or suggestions for improving this article.

← Converting circular structure to JSON -bash: nvm: command not found
Prakash Pradhan

Prakash Pradhan

Sr. Software Engineer

Senior Software Engineer with 10+ years of experience in designing and scaling distributed systems and full-stack applications. Experts in optimizing system performance, and delivering high-impact technical solutions across the entire software development lifecycle.

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