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I use LightDM als my display manager, entering user credentials via its greeter login. The system's PAM authenticates against a LDAP server. Unfortunately, the network is unreliable hence the LDAP server often cannot be reached. This is what is logged in auth.log:

lightdm: nss_ldap: could not connect to any LDAP server as (null) - Can't contact LDAP server
lightdm: nss_ldap: failed to bind to LDAP server ldap://ldap.example.com: Can't contact LDAP server
lightdm: nss_ldap: could not search LDAP server - Server is unavailable

Consequently, the LDAP PAM module fails. Unfortunately, the exact reason of the error is lost along the way and LightDM shows a "wrong password" message, which is horribly misleading:

Login screen shows "wrong password" due to network issues

Is there any way to display a "login failed due to LDAP server unreachable" message instead? This is a mock-up of what I would like to see:

mock-up of better error message in login screen

Further details:

  • I cannot guarantee that a user has ever been logged-on to any machine in particular.
  • A network connection is needed as the user's home resides on a share.
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    I would say you could probably change the message, but it looks like you get password message when auth fails for any reason. If you want it to react properly, you will have to file a bug with lightdm, or better, fix it yourself ;-)
    – thecarpy
    May 7 '19 at 12:33
  • @thecarpy I was afraid that would probably be the answer. I had hoped I might have overlooked some configuration directive or alike.
    – Hermann
    May 7 '19 at 12:34
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It seems your either using pam_ldap/nss_ldap combo or nss-pam-ldapd. Both do not support caching password hashes of former successful logins.

You might want to consider using sssd instead with password caching enabled.

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  • It is indeed pam_ldap. Your suggestion is a sensible workaround in theory – but the home directory is also mounted via network. I would prefer to inform the user of the actual problem.
    – Hermann
    May 19 '19 at 21:40
  • You did not mention LDAP-based automounter in your question at all.
    – Michael Ströder
    May 20 '19 at 11:08
  • Indeed, I did not. I added detail to the question.
    – Hermann
    May 20 '19 at 14:03

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