How to install Google authenticator on Centos/Ubuntu?

1. Add the EPEL repo

2. Install Google Authenticator

[email protected]:~ yum install google-authenticator

3. Run the initialization app.

[email protected]:~ google-authenticator

4. After you run the command, you’ll be asked a few questions.

Do you want authentication tokens to be time-based (y/n) y

Do you want me to update your "/root/.google_authenticator" file? (y/n) y

Do you want to disallow multiple uses of the same authentication

token? This restricts you to one login about every 30s, but it increases

your chances to notice or even prevent man-in-the-middle attacks (y/n) y

By default, a new token is generated every 30 seconds by the mobile app.

In order to compensate for possible time-skew between the client and the server,

we allow an extra token before and after the current time. This allows for a

time skew of up to 30 seconds between authentication server and client. If you

experience problems with poor time synchronization, you can increase the window

from its default size of 3 permitted codes (one previous code, the current

code, the next code) to 17 permitted codes (the 8 previous codes, the current

code, and the 8 next codes). This will permit for a time skew of up to 4 minutes

between client and server.

Do you want to do so? (y/n) y

If the computer that you are logging into isn't hardened against brute-force

By default, this limits attackers to no more than 3 login attempts every 30s.

Do you want to enable rate-limiting? (y/n) y

5. Configure openssh (SSHD)

[email protected]:~ vi /etc/pam.d/sshd

Scroll down to the bottom of the file and add the following line:

auth required pam_google_authenticator.so

6. Edit the SSH configuration file

[email protected]:~ vi /etc/ssh/sshd_config

Enable 2-factor Challenge Response Authentication:

ChallengeResponseAuthentication yes

#ChallengeResponseAuthentication no

7. Restart SSHD service

[email protected]:~ service sshd restart