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After some serious GRUB issues after routine kernel updates, forcing a grub-reinstall via chroot and some single-user mode maintenance, I now cannot login to my server (except via single-user mode)

When attempting to SSH to the server my connection is reset immediately after entering username - no password prompt is presented.

I've plugged in my monitor and keyboard to the headless server and when trying to login I received this message immediately after entering my username:

login: "PAM Failure, aborting: Critical error - immediate abort"

Again, no password prompt is displayed.

I am able to gain access via kernel recovery mode and login as root through single-user mode with networking. I've attempted a dpkg reconfigure believing I may have had some incomplete/borked packages, but to no avail.

Looking through /etc/pam.d/login doesn't seem to lead me in any obvious directions and I'm afraid I'm out of ideas.

Googling doesn't help me much, one guy reinstalled (really don't want to do this) and the rest I could find were old Gentoo related bugs.

Any tips?

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Anything in the logs? Poke around the recent files in /var/log and see if there are any clues. Googling for error messages often gets me a long way. – Hamish Downer Jun 6 '12 at 12:05
I didn't see anything obvious in the logs relating to this. I noticed that the "common-session" file in the /etc/pam.d/ folder had changed at date of breakage. I copied the file out of the LiveCD and in to my real install, but this didn't help either. Consequently, my server is up and running, storage is accessible, but I cannot authenticate AT ALL (meaning I can't login and no application running under my account are workable) – ThoughtCoder Jun 7 '12 at 1:43

Managed to fix the problem by booting from a LiveCD and copying all the files from the /etc/pam.d/ to my actual install and rebooted, fixing the problem. I did need to change my password with "passwd" to update the files accordingly.

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