sshd[902]: debug1:PAM: password authentication failed for an illegal user: Authentication failure

Troubleshooting PAM Authentication Failures: Illegal User Authentication in SSH

Overview: This article tackles SSH authentication failures due to pam_ldap configuration, specifically addressing errors such as "sshd[902]: debug1:PAM: password authentication failed for an illegal user: Authentication failure." It advises on adjusting /etc/ldap.conf for RFC 2307 mappings, restarting nscd, and verifying LDAP integration using getent passwd and finger commands.

If you are getting the error when you configured pam_ldap for the backend ssh authentication.

Ensure to uncomment following lines in /etc/ldap.conf

# RFC 2307 (AD) mappings
nss_map_objectclass posixAccount user
#nss_map_objectclass shadowAccount user
nss_map_attribute uid sAMAccountName
nss_map_attribute homeDirectory unixHomeDirectory

Restart the nscd service.

service nscd restart

The following commands should now return a result from AD/LDAP.

root@ubuntu:~# getent passwd james

james:*:10003:11000:james:/home/james:/usr/local/bin/ezsh

root@ubuntu:~# finger james

Login: james                     Name: james
Directory: /home/james                 Shell: /usr/local/bin/ezsh
On since Thu Feb 1 14:23 (IST) on pts/1 from 192.168.56.1
   1 hour 47 minutes idle
No mail.
No Plan.

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