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After a recent update in Arch Linux, which required updating /etc/passwd, /etc/shadow, and /etc/pam.d/login, I have started being prompted for my login password twice at boot up. I boot to runlevel 3, login, and start my window manager manually with startx. The prompt I'm talking about is in the basic shell.

I enter my username, then am prompted for my password, which I enter. Then an identical password prompt appears. I enter my password again, and am successfully logged in.

Any suggestions troubleshooting this?

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up vote 4 down vote accepted

There is a module in PAM that deals with user authentication called pam_unix.so. It will be mentioned in a file called common-auth or simply auth in the directory /etc/pam.d/. There may be multiple entry there or perhaps the update could have modified it in some way. Can you post the lines in the file here? If you cannot find it, you have to search for the file that is identical to common-auth in arch-linux.

You can read about pam and the modules.

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1  
This was, indeed, the problem. I cross-posted here and in the Arch forums; another explanation can be found there. An Arch update removed some items in /etc/pam.d/login and put them in /etc/pam.d/system-login which was called by /etc/pam.d/system-local-login. Since I incorrectly merged my existing login with the update pushed by Arch, pam_unix.so was indeed being called twice, hence two login prompts. – Hendy Sep 16 '12 at 20:09
    
Thanks for sharing Hendy. – paintbox Sep 17 '12 at 12:04

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