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We’ve open-sourced our duo_unix package for easy, drop-in two-factor authentication to any Unix system. Combined with our hosted service, it’s the simplest way to protect logins to your cloud or datacenter hosts with strong, out-of-band authentication. Here’s how:

1. Set up your Duo account

First, create your new Duo account at – it’s free for up to 10 users or for any open-source project!

In the Duo admin interface, create a new Unix integration for your host:


You’ll need the resulting integration and secret keys for your duo_unix configuration:


2. Set up login_duo on your Unix system

Next, on your Unix system, download, build and install the duo_unix distribution (or install the appropriate package for your OS: Debian, Ubuntu, etc.):


Once installed, edit /etc/duo/login_duo.conf as root to add your integration and secret keys:


Then as a regular user, test login_duo manually. If everything’s set up correctly, you’ll be prompted to enroll (or check your syslog for errors):


Enroll your phone:


The next time you run login_duo, you’ll be prompted to authenticate with your phone:


3. Enable login_duo on your Unix system

To enable Duo login for individual accounts using SSH pubkeys, use the authorized_keys command option. For example, to verify individual admins authorized to log into a shared root account:


* This also works for user-local installations (e.g. $HOME/bin) without root access in shared web hosting environments — just specify the location of login_duo.conf with -c.

Similarly, you can enable Duo login system-wide to follow any SSH login method (password, pubkey, etc.) for any user. Edit your /etc/sshd_config (or /etc/ssh/sshd_config) to add the following line:

ForceCommand /usr/local/sbin/login_duo

And optionally limit Duo login to a subset of users by UID or group in /etc/duo/login_duo.conf:

group = wheel

The duo_unix PAM configuration is similar if you’d like to protect other PAM-enabled daemons or programs (e.g. sudo).

Let us know if you have any questions or comments!

Dug Song
CEO & Co-Founder

Dug has a history of leading successful products and companies to solve pressing security problems. Dug spent 7 years as founding Chief Security Architect at Arbor Networks, protecting 80% of the world’s Internet service providers, and growing to $120M+ annual revenue before its acquisition by Danaher. Before Arbor, Dug built the first commercial network anomaly detection system (acquired by NFR / Check Point), and managed security in the world’s largest production Kerberos environment (University of Michigan).


Free Guide

Two-Factor Authentication Evaluation Guide

This guide walks through some of the key areas of differentiation between two-factor authentication solutions and provides some concrete criteria for evaluating technologies and vendors.


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