Lenovo ThinkPad T420. Fingerprint reader

Make sure you have one of the supported finger scanners. You can check if your device is supported by checking this list of supported devices. To check which one you have, type:
lsusb
Bus 001 Device 003: ID 147e:2016 Upek Biometric Touchchip/Touchstrip Fingerprint Sensor

Installation:
yum install fprintd ImageMagick

Login configuration
Note: If you use GDM, the fingerprint-option is already available in the login menu. You can skip this section!

Add pam_fprintd.so to the auth section of /etc/pam.d/system-auth and /etc/pam.d/system-auth-ac

vi /etc/pam.d/system-auth

auth required pam_env.so
auth sufficient pam_fprintd.so
auth sufficient pam_unix.so nullok try_first_pass
auth requisite pam_succeed_if.so uid >= 1000 quiet_success
auth required pam_deny.so

This tries to use fingerprint login first, and if if fails or if it finds no fingerprint signatures in the give user’s home directory, it proceeds to password login.

To add a signature for a finger, run

$ fprintd-enroll

You will be asked to scan the given finger. After that, the signature is created in /var/lib/fprint/$USER.

For more information, see man fprintd.

Links:
https://wiki.archlinux.org/index.php/Lenovo_ThinkPad_T420#Fingerprint_reader
https://wiki.archlinux.org/index.php/Fprint#Setup_fingerprint-gui
http://karuppuswamy.com/wordpress/2010/07/22/how-to-get-fingerprint-reader-working-in-fedora-linux-upek-147e1000-in-this-case/