I had this issue after installed Oracle Database 11g R2 in CentOS 5.9 64-bit.
I could not log in CentOS in runlevel 3, but runlevel 5 or ssh was OK.
View log : /var/log/secure, I saw:
Oct 15 08:16:58 db1 login: PAM unable to dlopen(/lib/security/pam_limits.so)
Oct 15 08:16:58 db1 login: PAM [error: /lib/security/pam_limits.so: wrong ELF class: ELFCLASS32]
Oct 15 08:16:58 db1 login: PAM adding faulty module: /lib/security/pam_limits.so
Oct 15 08:17:00 db1 login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)
Oct 15 08:17:00 db1 login: Module is unknown
I remembered when installed Oracle, i edited file /etc/pam.d/login.
Appended file with line : session required /lib/security/pam_limits.so (Oracle docs said that ..... )
But my CentOS is 64-bit, so I changed it to session required /lib64/security/pam_limits.so and try logging. And now everything is OK.
