Lock out users after n unsuccessful consecutive login attempts. The first sets of changes are made to the PAM configuration files. The second set of changes are applied to the program specific PAM configuration file. The second set of changes must be applied to each program that will lock out users. Check the documentation for each secondary program for instructions on how to configure them to work with PAM. Set the lockout number to the policy in effect at your site. Locking out user IDs after n unsuccessful consecutive login attempts mitigates brute force password attacks against your systems.
Edit the /etc/pam.d/common-auth file and add the following pam_tally2.so line: auth required pam_tally2.so onerr=fail audit silent deny=5 unlock_time=900 Edit the /etc/pam.d/common-account file and add the following pam_tally2.so line: account required pam_tally2.so Notes: Additional module options may be set, recommendation only covers those listed here. If a user has been locked out because they have reached the maximum consecutive failure count defined by deny= in the pam_tally2.so module, the user can be unlocked by issuing the command pam_tally2 -u <username> --reset. This command sets the failed count to 0, effectively unlocking the user. Use of the "audit" keyword may log credentials in the case of user error during authentication. This risk should be evaluated in the context of the site policies of your organization.