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On ubuntu 14.04, I had a problem with my user authenticating on a domain of my company over ldap, and the IT guy played about with some configuration files and packages. Now, on a local user, whenever I execute a command with sudo the prompt asks twice for a password.

I've been searching quite extensively through the Internet, and cannot find the solution. I've tried every possible solution: all the PAM configuration files have been reset, as well as /etc/nsswitch.conf. I have uninstalled and purged all the packages related to ldap, have checked /etc/hostsand /etc/sudoers... but the problem remains.

The only two significant clues that I can provide is that this only happens on the command line (if I execute synaptic from with the GUI, the system only asks me for the password once), and it seems, from /var/log/auth.log, that pam_unix.so is being invoked only once, so PAM seems to be ok.

How can I trace the origin of this problem?

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I've managed to solve my problem. What was confusing me is that I thought that

pam-auth-update --force

was overwriting completely all the PAM configuration files (/etc/pam.d/common-*), so that those files would end up as if they were brand new. But it does not. What pam-auth-updatedoes is to overwrite all the text of those files up to the last line of the default configuration file, which actually reads # end of pam-auth-update config (I had failed to realise that it was quite self-explanatory). Anything written by the user before that line is overwritten, but everything that appears after that line is not touched by the update.

For some reason the lines

@include common-auth
@include common-session
@include common-session-noninteractive

that are called by PAM when executing the service sudo, had been pasted at the very end of the common-session-noninteractive file, and updating PAM was not deleting them. They were making PAM ask for the password a second time.

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