Oracle Linux: Login Fails with " Access denied for user user by PAM account configuration [preauth]"

Applies to: 

Linux OS - Version Oracle Linux 6.0 and later 

 

Symptoms:  

While trying to login with a local user, the following is shown in /var/log/secure 

 hostname sshd[105661]:info: Postponed publickey for user from xx.xx.xx.xx port 2xxx6 ssh2 [preauth] 
 hostname sshd[105661]:info: Failed publickey for user from xx.xx.xx.xx port 2xxx6 ssh2: RSA SHA256:<hash> 
 hostname sshd[105661]:crit: fatal: Access denied for user user by PAM account configuration [preauth] 

furthermore messages like  

Authentication service cannot retrieve authentication info 

are displayed as well.  

Cause: 

/etc/nsswitch.conf had missing entries ( files ) in the shadow line