Yubico Pluggable Authentication Module (PAM)
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Yubico PAM module

The Yubico PAM module provides an easy way to integrate the Yubikey
into your existing user authentication infrastructure.  PAM is used by
GNU/Linux, Solaris and Mac OS X for user authentication, and by other
specialized applications such as NCSA !MyProxy.

Status and Roadmap

The module is working for multi-user systems. The primary mode of
operation is by doing online validation using a YubiKey validation
service (such as the YubiCloud, or a private one configured using
the 'url' parameter).

In version 2.6, offline validation was also made possible through
the use of HMAC-SHA1 Challenge-Response found in YubiKey 2.2 and
later. This has introduced a currently mandatory dependency of
libykpers-1 from the ykpersonalize package.

The development community is co-ordinated via Google Code :


The license for pam_yubico is the 2-clause BSD license, which is
compatible with the Linux-PAM BSD/GPL license.  See the file COPYING
for more information.

Building from Git

Skip to the next section if you are using an official packaged

You may check out the sources using Git with the following command:

   $ git clone git://github.com/Yubico/yubico-pam.git yubico-pam

This will create a directory 'yubico-pam'.

Autoconf, automake and libtool must be installed to create a compilable
source tree.

Generate the build system using:

   $ cd yubico-pam
   $ autoreconf --install


You will need to have libykclient (ykclient.h, libykclient.so) and
libpam-dev (security/pam_appl.h, libpam.so) installed.  Get the
ykclient library from:


It in turn requires Curl, which you need to have installed, and
libyubikey. Get libyubikey from


The new Challenge-Response offline authentication requires libykpers-1
from the yubikey-personalization project :


The build system uses Autoconf, to set up the build system run:


Use --without-ldap to disable ldap support.

Then build the code, run the self-test and install the binaries:

  make check install

Ubuntu PPA

There is an Ubuntu PPA (Private Package Archive) for yubico-pam that
can be installed using the following commands on reasonably modern
Ubuntu platforms :

  $ sudo add-apt-repository ppa:fredrikt/yubico-pam
  $ sudo apt-get update
  $ sudo apt-get install yubico-pam

You will have to configure pam_yubico manually in /etc/pam.d/common-auth
manually after installing.


Install it in your PAM setup by adding a line to an appropriate file
in /etc/pam.d/:

  auth sufficient pam_yubico.so id=16 debug

and move pam_yubico.so into /lib/security/ (or wherever PAM modules
live in your system) :

  mv /usr/local/lib/security/pam_yubico.so /lib/security/

For more information, see the project Wiki page.

Supported PAM module parameters are:

  "authfile":   to indicate the location of the file that holds the
                mappings of Yubikey token IDs to user names.

  "id":         to indicate your client identity.

  "key":        to indicate your client key in base64 format.
		The client key is also known as API key, and provides
		integrity in the communication between the client (you)
		and the validation server.
		If you want to get one for use with the default YubiCloud
		service, visit this URL :


  "debug":      to enable debug output to stdout.

  "alwaysok":   to enable all authentication attempts to succeed
                (aka presentation mode).

                Before prompting the user for their password, the module
                first tries the previous stacked module´s password in case
                that satisfies this module as well.

                The argument use_first_pass forces the module to use a previous
                stacked modules password and will never prompt the user - if no
                password is available or the password is not appropriate, the user
                will be denied access.

  "url":        specify the URL template to use, this is set by calling
                yubikey_client_set_url_template, which defaults to:




		depending on your version of yubico-c-client.

                This argument is used to show the OTP when it is entered,
		i.e. to enable terminal echo of entered characters.
                You are advised to not use this, if you are using two factor
                authentication because that will display your password on the

                This requires the service using the PAM module to
                display custom fields.  For example, OpenSSH requires
                you to configure "ChallengeResponseAuthentication no".

  "ldap_uri":   specify the LDAP server URI (e.g. ldap://localhost).

  "ldapserver": specify the LDAP server host (default LDAP port is used).
                _Deprecated.  Use "ldap_uri" instead._

  "ldapdn":     specify the dn where the users are stored
                (eg: ou=users,dc=domain,dc=com).

  "user_attr":  specify the LDAP attribute used to store user names (eg:cn).

  "yubi_attr":  specify the LDAP attribute used to store the Yubikey id.

  "capath":     Path to a directory with SSL CA certs you trust.

If you are using "debug" you may find it useful to create a
world-writable log file:

  touch /var/run/pam-debug.log
  chmod go+w /var/run/pam-debug.log

Authorization Mapping Files
A mapping must be made between the Yubikey token ID and the user ID it is
attached to. There are two ways to do this, either centrally in one file, or
individually, where users can create the mapping in their home directories.
If the central authorization mapping file is being used, user home directory
mappings will not be used and the opposite applies if user home directory
mappings are being used, the central authorization mappings file will not
be used.

Central authorization mapping

Create a /etc/yubikey_mappings, the file must contain a user name and the
Yubikey token ID separated by colons (same format as the passwd file) for
each user you want to allow onto the system using a Yubikey.

The mappings should look like this, one per line:

   <user name>:<Yubikey token ID>:<Yubikey token ID>:….
   <user name>:<Yubikey token ID>:<Yubikey token ID>:….

Now add authfile=/etc/yubikey_mappings to your PAM configuration line, so it
looks like:

   auth sufficient pam_yubico.so id=16 authfile=/etc/yubikey_mappings

Individual authorization mapping by user
Each user creates a ~/.yubico/authorized_yubikeys file inside of their home
directory and places the mapping in that file, the file must have only one

   <user name>:<Yubikey token ID>:<Yubikey token ID>

This is much the same concept as the SSH authorized_keys file.

Obtaining the Yubikey token ID (a.k.a. public ID)
You can obtain the Yubikey token ID in two places. One is by removing the
last 32 characters of any OTP generated with your Yubikey, the other
is by using the modhex calculator located here :


Enter your Yubikey OTP and convert it, your Yubikey token ID is 12 digits and listed as:

   Modhex encoded: XXXXXXX


If you want to use the Yubikey to authenticate you on linux console
logins, add the following to the top of /etc/pam.d/login:

   auth sufficient pam_yubico.so id=16 debug


If you want to discuss anything related to the Yubico PAM module,
please contact Simon Josefsson <simon@yubico.com>.