Linux: Thinking With Fingers

So begins the case testing. Upon attempting multiple authentication scenarios, I discovered:

  • The GDM login was not working
  • Terminal sudo commands would accept a finger swipe but then not run the command nor inform the user if the password was accepted or not
  • Graphical authenticators such as the one used to authenticate for the, “Add/Remove Software,” application accepted the finger swipe and subsequently authenticated
  • The, “Lock Screen,” would not accept. I subsequently followed specific instructions to enable GNOME Screensaver functionality, but did not test again (what can I say, I am easily side-tracked…)

I figured this was not a GDM issue but instead a PAM issue because GDM was accepting the finger swipe properly, it was just saying the information was wrong. Somewhere along the way between PAM and GDM something was getting mangled. I looked back at the instructions I followed for any, “black boxes,” where commands are entered and things magically happen. I only had one: the pam.d config command.

Upon re-reading the instructions as well as glancing at instructions for other versions of Ubuntu, I noticed that Jaunty was the only one with this black box command. I opened up my /etc/pam.d/common-auth file and noticed that the changes made by the script included new-style syntax for pam.conf files. One part in particular was different: in other instructions you are told to use “required,” on the line including pam_unix.so, but the script I ran changes the line to say [success=1 default=ignore]. Taking a shot in the dark, I replaced that with, “required,” and rebooted.

It worked. For naysayers out there, I know this is a completely uneducated hack. I don’t fully understand the pam.conf syntax (nor the model as a whole), but from my quick reading I noticed that the new-style syntax I had just removed can still be represented by the old-style syntax I inserted. And it works. I hope this helps someone out there who was having the same problem as me. If I notice adverse side affects of my hack, I will go ahead and write about them here.

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