/var/log/faillog is a log file for failed login attempts. This file maintains a count of login failures and the limits for each account. The file is fixed length record, indexed by numerical ID. Each record contains the count of login failures since the last successful login; the maximum number of failures before the account is disabled; the line the last login failure occurred on; and the date the last login failure occurred. Since data is in binary format you need to use faillog command to display failed login attempt.
How do I use faillog?
To display failed login attempt for user root with following command:
$ faillog -u root
Login Failures Maximum Latest On root 0 0 02/17/06 14:49:52 +0530 tty1
To display all failed login attempt try:
$ faillog -a
Login Failures Maximum Latest On root 0 0 02/17/06 14:49:52 +0530 tty1 rocky 0 0 02/27/06 22:05:03 +0530 tty1 usr1 2 0 02/16/06 15:05:01 +0530 tty2