"pam_unix(lightdm:auth): conversation failed" on first login attempt

[Yvan Masson]

Dear maintainers,

I have set up Xubuntu 14.04 computers in a Active Directory environnement, using sssd. Everything is working well, except sometimes authentication with lightdm:

Here are the messages I have in /var/log/auth.log :

Mar 5 09:12:12 profs-04u lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "masson"
Mar 5 09:12:12 profs-04u lightdm: pam_unix(lightdm:auth): conversation failed
Mar 5 09:12:12 profs-04u lightdm: pam_unix(lightdm:auth): auth could not identify password for [masson]
Mar 5 09:12:12 profs-04u lightdm: pam_sss(lightdm:auth): authentication failure; logname= uid=0 euid=0 tty=:0 ruser= rhost= user=masson
Mar 5 09:12:12 profs-04u lightdm: pam_sss(lightdm:auth): received for user masson: 7 (Authentication failure)
Mar 5 09:12:12 profs-04u lightdm: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory
Mar 5 09:12:12 profs-04u lightdm: PAM adding faulty module: pam_kwallet.so
Mar 5 09:12:12 profs-04u lightdm: pam_succeed_if(lightdm:auth): requirement "user ingroup nopasswdlogin" not met by user "masson"
Mar 5 09:13:04 profs-04u lightdm: pam_unix(lightdm:auth): authentication failure; logname= uid=0 euid=0 tty=:0 ruser= rhost= user=masson
Mar 5 09:13:06 profs-04u lightdm: pam_sss(lightdm:auth): authentication success; logname= uid=0 euid=0 tty=:0 ruser= rhost= user=masson
Mar 5 09:13:06 profs-04u lightdm: pam_unix(lightdm-greeter:session): session closed for user lightdm
Mar 5 09:13:07 profs-04u lightdm: pam_unix(lightdm:session): session opened for user masson by (uid=0)

As you can see here, the first attempt fails because of "pam_unix(lightdm:auth): conversation failed". The second one is working.

Indeed, if the first login fails, the second one will always work. I also never had this problem if someone already authenticated on the computer.

The problem appears randomly:
 - it appears sometimes if I try to login just after boot, and also sometimes if I wait two hours after boot.
 - if I boot many computers in the same time (all configured the same way), and then try to authenticate on these with the same login, it will succeed on some and fail on others

I know this problem can come from many another components and configurations (network, sssd, kerberos,...), but I reported this bug against lightdm because it is the only place I found a significative error message. If you could tell me what "pam_unix(lightdm:auth): conversation failed" means, I could search for the origin of this issue.

Also, do not hesitate to ask for more informations.

Thanks,
Yvan