PAM triggers requests to LDAP server even when NSCD is configured

["saikiran.reddy [at] wipro.com" <saikiran.reddy [at] wipro.com>]

Hi,

  Am facing an issue when using nscd (for caching) with nslcd. Details below. Am following the setup steps as per the guidelines at https://arthurdejong.org/nss-pam-ldapd/setup.

  

  Appreciate if you could point me in the right direction..

 

 Problem:

------------

  With nscd configured, the expectation was that the nslcd would not send further requests to the ldap  server until the “positive-time-to-live” (configured in nscd.conf) expires. Have analyzed the wireshark captures and noticed that it is not the case.

 

  Details:

--------------

  WITHOUT NSCD:

1.       User attempts to login by providing the username.

2.       SSHD checks for the presence of the user in local files, does not find it (since the users are ldap) and queries the LDAP server

3.       LDAP server returns a success.

4.       SSH starts the PAM (UsePAM = yes, in sshd.conf) and prompts the user to enter the password.

5.       User enters the passwd

6.       PAM triggers the ldap search request (similar content as done in step 2 !!) to the ldap server

7.       Same as step 3.

8.       SSH login available to user.

9.       The above steps occur for all subsequent logins of the user.

  WITH NSCD:

1.       Steps 1-8 same as above in the FIRST iteration.

2.       Second and subsequent iteration until “positive-time-to-live”, ONLY step 2 DOES not happen, but steps 6 & 7 are happening. As per my understanding that should not be the case. Could you please confirm?

 

CONFIG/Ver:

------------------

Following are the details of the versions and the config files of nsswitch, nscd and pam.d/ for your reference.

Using Nslcd – 0.9.5

 

root@ep:~# cat /etc/nsswitch.conf

# /etc/nsswitch.conf

passwd:         files ldap

group:          files ldap

shadow:         files ldap

 

root@ep:~# cat /etc/nscd.conf

        enable-cache            passwd          yes

        positive-time-to-live   passwd          6000

        negative-time-to-live   passwd          20

        suggested-size          passwd          211

        check-files             passwd          yes

        persistent              passwd          yes

        shared                  passwd          yes

        max-db-size             passwd          33554432

        auto-propagate          passwd          yes

 

.. same for group, services, netgroup

 

pam.d/common-account

account   required    pam_unix.so                                        

account   sufficient  pam_ldap.so minimum_uid=1000                         

account   required    pam_permit.so

 

pam.d/common-auth

auth      sufficient  pam_ldap.so minimum_uid=1000

auth      sufficient  pam_unix.so nullok try_first_pass

auth      required    pam_deny.so

 

pam.d/common-password

password  sufficient  pam_unix.so nullok md5 shadow use_authtok

password  sufficient  pam_ldap.so minimum_uid=1000 try_first_pass        

password  required    pam_deny.so    

 

pam.d/common-session

session   required    pam_unix.so

session   optional    pam_ldap.so minimum_uid=1000

session   required    pam_mkhomedir.so skel=/etc/skel umask=0022

 

Thanks,

Sai

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