Using RADIUS to authenticate ssh users

Install the PAM RADIUS authentication module
$ sudo aptitude install libpam-radius-auth

Setup RADIUS server infomation
$ vi /etc/pam_radius_auth.conf
#server[:port]    shared_secret    timeout
Server_IP    SHARED_SECRET    3

Setup PAM
$ vi /etc/pam.d/common-auth

##### RADIUS ######
auth    sufficient          pam_radius_auth.so debug
account required            pam_radius_auth.so
session required            pam_radius_auth.so

##### Origin #####
auth    [success=1 default=ignore]  pam_unix.so nullok_secure
auth    requisite           pam_deny.so
auth    required            pam_permit.so

##### automatic home directory creation for RADIUS user login #####
session required            pam_mkhomedir.so skel=/etc/skel/ umask=0022 silent


Create user without password for RADIUS authentication, and assign to admin for sudo
$ sudo useradd RADIUS_user -G admin