If a wrong password is entered into kdm, it forces the user to wait for some seconds for the next attempt. While this is reasonable, there might be several reasons to switch this off, e.g. the use of pam_tally. This is my pam.d/common-auth on openSUSE: ################################################################ auth required pam_env.so auth required pam_unix.so nodelay nullok try_first_pass ################################################################ The nodelay "discourage[s] the authentication component from requesting a delay should the authentication as a whole fail", according to the pam_unix manpage. Unfortunatelly it appears that kdm doesn't honor this discouragement. Reproducible: Always Steps to Reproduce: 1. Add "nodelay" option to pam_unix 2. Enter wrong password in kdm Actual Results: kdm blocks for a few seconds Expected Results: While stating somewhere on the screen that authentication failed, the user should immediately be allowed to reenter the password. I'm running openSUSE 12.3, with kdm version 4.10.3-1.37.7 and the "horos" theme. In contrast to kdm, agetty on tty1--6 honors the nodelay option and doesn't block after a failed authentication. Since it seems to be relevant for some applications, I also set FAIL_DELAY to 0 in /etc/login.defs, but it didn't help.
KDM is unmaintained and not used in KDE Plasma 5. SDDM is the login manager used in KDE Plasma 5. If you still have this same issue with SDDM, please file an issue on the SDDM bugtracker (after doing a search for existing issues first!): https://github.com/sddm/sddm/issues/